Extreme Insects
Richard Jones
Insects are the most extreme organisms on Earth and, despite their diminutive size, they wield inordinate power. With the exception of the polar icecaps, every terrestrial ecosystem on earth is colonized by them, and they account for almost three-quarters of all named animals – that's one million species at the last count!This book is a celebration of the insect universe, exploring their amazing forms and functions, their fascinating behaviour and the enormous impact they have on our lives. With its lively and informative text, it looks at insects in all their extremes, from the biggest, fastest and fiercest to the best nest builder, most devious hunter and deadliest bride.Insects are extreme in numbers – a single leaf-cutter ant nest, the size of a large camper van, may contain seven million individuals working together as a single giant super-organism. Insects are extreme in their bizarre forms – the stalk-eyed fly, as its name suggests, carries its eyes on the end of two ludicrously long stalks. And insects are invariably extreme in behaviour – take for instance the giraffe-necked weevil that holds head-bobbing contests to win a mate. Yet there is always method in their apparent madness, as each strange form and function is an adaptation designed to solve the extreme pressures that arise through the struggle to survive in a world that is always dangerous, competitive and unforgiving.
Extreme Insects
Richard Jones
This book is for my parents. My father, Alfred Jones,
from whom I acquired my love of natural history, gave
me a precious gift – the thirst for knowledge. My
mother, Rosamond Jones, gave me the time and her
tolerance, whilst I tried to quench it.
Contents
Introduction (#u8547af98-3ec0-571e-9aca-87d9c4015366)
Extreme From (#uf0f30301-549d-579e-9b1c-af7fc6e67b69)
Oldest insect (#ulink_a6db44fa-0020-5ae4-b487-33d64d658f09)
Biggest insect (#ulink_a9784f4f-cfb1-5396-8db0-79a17417c48b)
Longest insect (#ulink_a05f2f17-1116-58da-9fb7-b16f630169af)
Whitest insect (#ulink_6aec2a30-0720-5e1d-82d5-2d0b6781cb70)
Shiniest insect (#ulink_7b771a94-edb3-55aa-9ae3-7d1ac60ddf86)
Slimiest insect (#ulink_19489622-00a4-5754-82f4-41f3c6104a54)
Biggest blockhead (#ulink_dab98c31-7649-5aed-aed9-babe685ba06e)
Most sexually dimorphic insect (#ulink_de256d9a-bec5-536b-ae4a-e7d3895458ad)
Most mixed-up sexuality (#ulink_15da5a00-fa74-5dcd-aad4-1b63131e1264)
Most bloated insect (#ulink_9e81374d-a2ca-5bda-b045-bb1f71ed3c0c)
Most seasonally dimorphic insect (#ulink_a89857fd-586a-5191-ad44-c343f481eec5)
Highest number of wings (#ulink_1b733b56-9389-5059-9921-9589e38c2cb1)
Flattest insect (#ulink_9ce322cf-8603-528d-8851-1d6f89622e33)
Most back-to-front insect (#ulink_a90d3fd2-da8f-580d-8bfb-fe149842130c)
Longest ovipositor (#ulink_f0f3e47a-33b6-5903-bf6f-90840e936463)
Widest head (#ulink_d579b8dd-3abb-5df8-8b5a-6de217db7c9f)
Brightest light generation (#ulink_59a13a98-609f-53ab-ba11-684040fe4aa4)
Most variable colour pattern (#ulink_f4831d83-49b1-507f-87ed-ebfe226a68f5)
Bloodiest insect (#ulink_e8817f37-18a7-5212-9e21-e7195bfad4d7)
Most beautiful insect (#ulink_617f696b-e53c-5043-8a95-e882b8e3ca8e)
Longest head (#ulink_0a0993b3-be4d-51cf-a1db-630696125c2f)
Most streamlined insect (#ulink_7878e700-d3f9-53c4-a45b-d502a55afbb0)
Loudest insect (#ulink_75efc260-1f61-5918-9224-b0a13a4fe564)
Best hoverer (#ulink_abcd8e26-4c98-5582-b7e3-da7b61caa27a)
Ugliest insect (#ulink_3e1cecc3-4d40-52fd-993c-4da4d107973a)
Largest jaws (#ulink_870d9a2c-d89f-5959-85bc-9818cbeb314c)
Largest wingspan (#litres_trial_promo)
Best camouflage (#litres_trial_promo)
Most transparent wings (#litres_trial_promo)
Hairiest legs (#litres_trial_promo)
Snappiest jaws (#litres_trial_promo)
Prettiest eyes (#litres_trial_promo)
Most elegant eggs (#litres_trial_promo)
Largest eye markings (#litres_trial_promo)
Lightest footstep (#litres_trial_promo)
Furriest insect (#litres_trial_promo)
Most poisonous insect (#litres_trial_promo)
Most heavily armoured insect (#litres_trial_promo)
Longest wing tails (#litres_trial_promo)
Best burrower (#litres_trial_promo)
Smallest insect (#litres_trial_promo)
Heaviest insect (#litres_trial_promo)
Fastest flier (#litres_trial_promo)
Fastest runner (#litres_trial_promo)
Longest tongue (#litres_trial_promo)
Smelliest insect (#litres_trial_promo)
Most subterranean insect (#litres_trial_promo)
Fastest wing-beat (#litres_trial_promo)
Smallest egg (#litres_trial_promo)
Largest egg (#litres_trial_promo)
Spikiest insect (#litres_trial_promo)
Biggest feet (#litres_trial_promo)
Largest claws (#litres_trial_promo)
Extreme Evolution (#litres_trial_promo)
Most punctual insect (#litres_trial_promo)
Giddiest insect (#litres_trial_promo)
Most useful young (#litres_trial_promo)
Best mutual coexistence (#litres_trial_promo)
Largest overwintering congregation (#litres_trial_promo)
Largest colony (#litres_trial_promo)
Most generous nuptial gift (#litres_trial_promo)
Best passenger (#litres_trial_promo)
Most necrophilic insect (#litres_trial_promo)
Cleverest digger (#litres_trial_promo)
Most violent sex act (#litres_trial_promo)
Biggest plant distortion (#litres_trial_promo)
Best thermometer (#litres_trial_promo)
Best architect (#litres_trial_promo)
Cleverest drinker (#litres_trial_promo)
Most dangerous egg-laying strategy (#litres_trial_promo)
Most adventurous insect (#litres_trial_promo)
Most disgusting habits (#litres_trial_promo)
Most cold-tolerant insect (#litres_trial_promo)
Most devious prey trap (#litres_trial_promo)
Most untrusting sex act (#litres_trial_promo)
Best sculptor (#litres_trial_promo)
Most unusual foodstuff (#litres_trial_promo)
Most extreme metamorphosis (#litres_trial_promo)
Best eyesight (#litres_trial_promo)
Best mimic (#litres_trial_promo)
Biggest migration (#litres_trial_promo)
Best wrestler (#litres_trial_promo)
Largest swarm (#litres_trial_promo)
Longest-lived adult (#litres_trial_promo)
Shortest larval stage (#litres_trial_promo)
Best kicker (#litres_trial_promo)
Most organised society (#litres_trial_promo)
Most unsavoury defecation behaviour (#litres_trial_promo)
Shortest-lived adult (#litres_trial_promo)
Most explosive insect (#litres_trial_promo)
Longest sperm (#litres_trial_promo)
Largest parasite (#litres_trial_promo)
Highest heat tolerance (#litres_trial_promo)
Most diverse life histories (#litres_trial_promo)
Most bizarre reverse metamorphosis (#litres_trial_promo)
Longest larval stage (#litres_trial_promo)
Best jumper (#litres_trial_promo)
Best dancer (#litres_trial_promo)
Best thief (#litres_trial_promo)
Most patient insect (#litres_trial_promo)
Best sunbathing protection (#litres_trial_promo)
Most widespread insect (#litres_trial_promo)
Extreme Impact (#litres_trial_promo)
Most useful scientific research tool (#litres_trial_promo)
Most painful sting (#litres_trial_promo)
Most revered insect (#litres_trial_promo)
Most boring insect (#litres_trial_promo)
Most eaten by humans (#litres_trial_promo)
Most (un)wanted (#litres_trial_promo)
Best human aphrodisiac (#litres_trial_promo)
Most confusing insect (#litres_trial_promo)
Most sinister insect (#litres_trial_promo)
Most misplaced insect (#litres_trial_promo)
Oldest surviving insect specimen (#litres_trial_promo)
Most bewitching insect (#litres_trial_promo)
Most important averted plague (#litres_trial_promo)
Most unusually represented in art (#litres_trial_promo)
Most musical insect (#litres_trial_promo)
Most helpful clean-up (#litres_trial_promo)
Worst plague (#litres_trial_promo)
Most unusual mode of range extension (#litres_trial_promo)
Most embarrassing insect (#litres_trial_promo)
Most dangerous insect (#litres_trial_promo)
Most valuable service (#litres_trial_promo)
Most diverse insect fauna (#litres_trial_promo)
Most irritating insect (#litres_trial_promo)
Most valuable insect product (#litres_trial_promo)
Most medically useful insect (#litres_trial_promo)
Most dermatologically useful insect (#litres_trial_promo)
Most dramatic recovery from near-extinction (#litres_trial_promo)
Most forensic insect (#litres_trial_promo)
Worst infestation of a person (#litres_trial_promo)
Best example of evolution in action (#litres_trial_promo)
Most endangered species (#litres_trial_promo)
Most destructive insect (#litres_trial_promo)
Most diverse group (#litres_trial_promo)
Rarest insect (#litres_trial_promo)
Index (#litres_trial_promo)
Stop Press (#litres_trial_promo)
Acknowledgements (#litres_trial_promo)
Copyright (#litres_trial_promo)
About the Publisher (#litres_trial_promo)
Introduction (#u75ec6138-982b-578e-9e1f-be73b83b3e3b)
Insects are the most extreme organisms on Earth, and despite their diminutive stature, they wield inordinate power. With the exception of the polar ice caps, every terrestrial ecosystem on Earth is colonised by insects and to some extent controlled by them (and they have made inroads onto the open ocean, too). They dominate the middle ground of virtually every terrestrial food chain or food web.
Insects are extreme in numbers. A single leaf-cutter ant nest, the size of a large camper van buried in the soil, may contain 8 million individuals working together as a single giant super-organism. In the tropical rainforests, termites can reach densities of 10,000 per square metre, a higher density of animal mass than in the largest wildebeest herds of the Serengeti. To produce such numbers, insects are extreme in their fecundity. Egg loads can be counted in thousands and generation times in days. If conditions are right, plagues of biblical proportions can appear as if spontaneously.
Insects are extreme in diversity. Even the experts cannot agree whether there are 3 million different species of insect on the Earth, 10 million, 30 million or 80 million. Compare that to the mere 5,400 known species of mammal. About four-fifths of all the animals yet discovered on our planet are insects: that’s over 1 million species at the last count. And there are many times that number out there awaiting discovery.
Insects are extreme in form. Evolved into the most peculiar shapes and colours, with strange structures and beautiful patterns, even the smallest of these wonderful creatures is magnificent under the microscope. Each has adapted to solve the extreme pressures that arise in the struggle to survive in a world that is dangerous, competitive and unforgiving.
Extreme Insects is divided into three chapters, exploring the nature of the insect universe and looking at some of the most extraordinary creatures in existence.
Extreme Form. In addition to the biggest, smallest, and largest wingspan, we take a look at extreme shapes: spikiest, furriest, shiniest, flattest. Why have such forms evolved? What benefit do they give to the insects that possess them?
Extreme Evolution. Some parts of insect anatomy can appear completely alien to the human eye. They have evolved to allow their possessors a special tool, weapon or means of escape. They have allowed certain insects to survive in extremely difficult or dangerous circumstances. Insects are complex creatures that interact with each other, with their food and with enemies who see them as food. And they get up to some very strange things. They seem to be dancing, skulking or hiding. They brave danger or run like cowards. Some nurture and some murder; some commit suicide. They may appear very clever or extremely dim. Some steal and some give gifts. What is the biological explanation behind these apparently odd behaviours?
Extreme Impact. Humans now reckon themselves to be the dominant life form on Earth, but we have been around for only a few hundred thousand years. Insects were here over 300 million years earlier. Humans, the mere junior upstarts, now come into conflict with a much older and better-established group of organisms. And despite our modern sophistication, we cannot escape such tenacious and apparently determined animals. They invade our fields, our houses and even our bodies. Some we can tame for our own uses, but with others we are still at war.
Insects are both awful and awe-inspiring, certainly worthy of our respect and our study. They give us a window on the natural world through which we can see, and attempt to understand, the environment in which we live, indeed of which we are an integral part. The huge numbers of insects, and their depredations on human food and health, are sometimes bemoaned. In reality, they form a vast biomass, and it is a wasteful shame that insects form an insignificant part of the human diet. We may not eat them very often, but insects offer a more philosophical sustenance – food for thought. In their study, there is a veritable feast for the mind.
Richard Jones
London, September 2009
Extreme Form (#u75ec6138-982b-578e-9e1f-be73b83b3e3b)
Oldest insect (#ulink_a6db44fa-0020-5ae4-b487-33d64d658f09) • Biggest insect (#ulink_a9784f4f-cfb1-5396-8db0-79a17417c48b) • Longest insect (#ulink_a05f2f17-1116-58da-9fb7-b16f630169af) • Whitest insect (#ulink_6aec2a30-0720-5e1d-82d5-2d0b6781cb70) • Shiniest insect (#ulink_7b771a94-edb3-55aa-9ae3-7d1ac60ddf86) • Slimiest insect (#ulink_19489622-00a4-5754-82f4-41f3c6104a54) • Biggest blockhead (#ulink_dab98c31-7649-5aed-aed9-babe685ba06e) • Most sexually dimorphic insect (#ulink_de256d9a-bec5-536b-ae4a-e7d3895458ad) • Most mixed-up sexuality (#ulink_15da5a00-fa74-5dcd-aad4-1b63131e1264) • Most bloated insect (#ulink_9e81374d-a2ca-5bda-b045-bb1f71ed3c0c) • Most seasonally dimorphic insect (#ulink_a89857fd-586a-5191-ad44-c343f481eec5) • Highest number of wings (#ulink_1b733b56-9389-5059-9921-9589e38c2cb1) • Flattest insect (#ulink_9ce322cf-8603-528d-8851-1d6f89622e33) • Most back-to-front insect (#ulink_a90d3fd2-da8f-580d-8bfb-fe149842130c) • Longest ovipositor (#ulink_f0f3e47a-33b6-5903-bf6f-90840e936463) • Widest head (#ulink_d579b8dd-3abb-5df8-8b5a-6de217db7c9f) • Brightest light generation (#ulink_59a13a98-609f-53ab-ba11-684040fe4aa4) • Most variable colour pattern (#ulink_f4831d83-49b1-507f-87ed-ebfe226a68f5) • Bloodiest insect (#ulink_e8817f37-18a7-5212-9e21-e7195bfad4d7) • Most beautiful insect (#ulink_617f696b-e53c-5043-8a95-e882b8e3ca8e) • Longest head (#ulink_0a0993b3-be4d-51cf-a1db-630696125c2f) • Most streamlined insect (#ulink_7878e700-d3f9-53c4-a45b-d502a55afbb0) • Loudest insect (#ulink_75efc260-1f61-5918-9224-b0a13a4fe564) • Best hoverer (#ulink_abcd8e26-4c98-5582-b7e3-da7b61caa27a) • Ugliest insect (#ulink_3e1cecc3-4d40-52fd-993c-4da4d107973a) • Largest jaws (#ulink_870d9a2c-d89f-5959-85bc-9818cbeb314c) • Largest wingspan (#litres_trial_promo) • Best camouflage (#litres_trial_promo) • Most transparent wings (#litres_trial_promo) • Hairiest legs (#litres_trial_promo) • Snappiest jaws (#litres_trial_promo) • Prettiest eyes (#litres_trial_promo) • Most elegant eggs (#litres_trial_promo) • Largest eye markings (#litres_trial_promo) • Lightest footstep (#litres_trial_promo) • Furriest insect (#litres_trial_promo) • Most poisonous insect (#litres_trial_promo) • Most heavily armoured insect (#litres_trial_promo) • Longest wing tails (#litres_trial_promo) • Best burrower (#litres_trial_promo) • Smallest insect (#litres_trial_promo) • Heaviest insect (#litres_trial_promo) • Fastest flier (#litres_trial_promo) • Fastest runner (#litres_trial_promo) • Longest tongue (#litres_trial_promo) • Smelliest insect (#litres_trial_promo) • Most subterranean insect (#litres_trial_promo) • Fastest wing-beat (#litres_trial_promo) • Smallest egg (#litres_trial_promo) • Largest egg (#litres_trial_promo) • Spikiest insect (#litres_trial_promo) • Biggest feet (#litres_trial_promo) • Largest claws (#litres_trial_promo)
Oldest insect (#u75ec6138-982b-578e-9e1f-be73b83b3e3b)
Most insects are very small, very delicate and very edible, so the fossil record they have left behind is extremely poor. The majority end up as prey for other animals, bitten, chewed and digested away. Where their remains are not eaten, there are no large bones to be preserved, and even the toughest of insect shells are made of highly biodegradable compounds. As a result, it takes some pretty special circumstances for insect fossils to form, and they are thoroughly scrutinised when found. Or at least they should be.
Until recently, the oldest acknowledged insect-like fossil was an ancient relative of modern springtails. These are wingless soft-bodied creatures that are not now classed as insects but as a sister group within the subphylum Hexapoda (six-legged arthropods). The fossil was found in 1919 by the Reverend W. Cran in the old red sandstone deposits (also called the Rhynie cherts) at Rhynie in Aberdeenshire, Scotland, which date from 407-396 million years ago. It was finally described in 1926 by three paleontologists, S. Hirst, S. Maulik and D.J. Scourfield, who aptly named it Rhyniella praecursor.
Two years later the rock sample was re-examined by the Australian entomologist Robin Tillyard. He identified what had been thought to be a broken fragment of a Rhyniella head capsule as belonging to a different creature, which he named Rhyniognatha hirsti.
The specimen lay untouched in the Natural History Museum, London, until 2004, when it was examined again by evolutionary entomologists Michael Engel and David Grimaldi. Using modern microscopes, they were able to see the fossilised jaws in much greater detail, and made an astonishing discovery. The shape of the jaws – toothed, broadly triangular, with two bulges where they articulated against other sections of the mouthparts – showed that they were not from some ancient springtail, but from a true insect and probably one with wings.
The Rhynie cherts formed in an area of hot springs and active geysers, which contained fluids rich in dissolved silica. As the water cooled the silica crystallised out of the water to form the fossils for which the area is now renowned. Hot water is very damaging to insect wings and other soft tissues, so it is not surprising that only the tough jaws of this insect have been preserved.
Biggest insect (#u75ec6138-982b-578e-9e1f-be73b83b3e3b)
In 1771, the Swedish naturalist Carolus Linnaeus described a giant beetle, and named it using his new scheme of binomial (two names) nomenclature: one name for the genus (Titanus) and one name for the species (giganteus). This name could not have been more apt for an insect that regularly reaches 17 cm (6.7 in) long. Linnaeus never saw the beetle itself. He coined the name after seeing an engraving of it in an encyclopedia.
The reason Linnaeus never saw one is that this was one of the rarest insects then known. During the 18th century, specimens were occasionally washed up dead on the shores of the Rio Negro, near Manaos in Brazil. The first living beetles were not found until 1958, when they were attracted to the street lights which were newly installed in the towns and villages in the area. Its early stages and life history are still unknown, but similar species have maggot-like larvae that feed in rotten logs.
There is still some doubt as to whether Titanus giganteus truly is the ‘largest’ insect. Few reliable measurements of living specimens have been taken. There is also little data regarding its weight – usually regarded as the key indicator of size by record-measuring organisations. As a result, four other beetles are contenders for the title. These are the shorter but stouter ‘Elephant’ beetles from South America – Megasoma actaeon (13.5 cm) and M. elephas (13.7 cm) – and the Goliath beetles from Africa – Goliathus regius (11 cm) and G. goliathus (11 cm).
Longest insect (#u75ec6138-982b-578e-9e1f-be73b83b3e3b)
One of the best ways to avoid being eaten is to hide, and one of the best ways to hide is to blend in with the surroundings using camouflage. Stick insects (also called walking sticks) have taken this to an extreme, and their pencil-thin bodies and pin-thin legs perfectly resemble the twigs through which they climb. So good at hiding have they become that some stick insects have acquired a trait that is a common evolutionary result of having no (or virtually no) predators – they have become very large.
For nearly 100 years, the record for the longest insect in the world was held by a specimen of a giant stick insect from Borneo, Phobaeticus (formerly Pharnacia) kirbyi. Its body was 328 mm (12.9 in) long, and from the tip of the outstretched front leg to the end of the back leg it measured 499 mm (19.6 in). This specimen had long been misidentified as the closely related P. serratipes, and it was only shortly after its true identity was established in 1995 that another huge stick insect was discovered. Ironically, this time it was a specimen of the true P. serratipes, found in Malaysia. It had a total length of 555 mm (21.9 in), although its body alone was slightly shorter than the famous P. kirbyi specimen.
Measuring lanky insects is fraught with difficulties, and this could have been the point at which some controversy arose. Most size measurements for insects deliberately ignore legs, antennae, tails and snouts because they vary tremendously within a population, especially between male and female of the same species. It has long been known that the leg lengths of stick insects vary, even when measured on different sides of the same specimen. However, the matter was settled in October 2008, with the description of a new species of stick insect from the Malaysian state of Sabah on the island of Borneo. Phobaeticus chani was named after the entomologist Datuk Chan Chew Lun, who donated the largest of three specimens, found by a local collector, to the Natural History Museum in London. With a body length of 357 mm (14 in) and a total length of 566 mm (22.3 in), it takes the record no matter which way it is measured.
Whitest insect (#u75ec6138-982b-578e-9e1f-be73b83b3e3b)
White is not a common insect colour, as it makes an insect stand out to predators in a natural world dominated by browns and greens. Perhaps the best-known white insects are cabbage whites (Pieris species). Like other butterflies, they use their colour patterns to recognise each other when mating. But they fade into insignificance against ghost beetles in the genus Cyphochilus.
Ghost beetles are found throughout Southeast Asia, where they are sometimes regarded as a pest in sugar cane plantations. Ghost beetle larvae feed in fungi, and the beetles’ whiteness is thought to be a camouflage against this rare white foodstuff. On close examination, the whiteness is caused not by the beetle’s exoskeleton (its tough outer shelllike body), which is dark brown and almost black, but by a dusty coating of pure white overlapping scales, which cover its body, head and legs. Each scale is minute, measuring only 250 by 100 μm and just 5 μm thick (a μm or micrometre is one thousandth of a millimetre).
The scales were first studied by Pete Vukusic, an optical physicist at Exeter University in the UK, who discovered that the beetles’ whiteness is caused by a random network of tiny filaments, 0.25 μm in diameter, inside the scale. The random arrangement of the filaments means that the different rainbow colours in natural white light are scattered simultaneously, equally and highly efficiently, with no single colour predominating. The beetles are among the whitest objects found in nature – much whiter than teeth and milk.
Shiniest insect (#u75ec6138-982b-578e-9e1f-be73b83b3e3b)
Insect colours serve many purposes. Greens and browns act as camouflage against living and dead leaves, tree trunks, branches and twigs. Bright yellow, orange and red, often marked with black, warn that an individual is poisonous or might sting. But the brightest and most spectacular colours do neither. Metallic glints of bronze, blue, green, red and violet occur in many beetles, bees, wasps, flies and, of course, butterflies (see page 48). The most astonishing of these are the brilliantly shining golden chafers, Plusiotis species, of Central and South America.
Metallic sheens are not colours in the conventional sense of a pigment or colourant on the surface of the animal. The red of a ladybird, for instance, appears because the yellow, green and blue wavelengths in sunlight are absorbed and only red light reflects back into the eye of the beholder. The metallic shine of the golden chafers, by contrast, is caused by the white sunlight being broken, much as it is when shining through a diamond, to give a series of rainbow glints.
Seen through an electron microscope, the surface of the beetle is revealed to be covered with minute parallel grooves. These reflect certain portions of the light at the precise angle to shine like polished metal, while absorbing and scattering other wavelengths.
Shining colours are not just for showing off to a potential mate, although this is important for many butterflies. One of the main purposes, ironically, may be to avoid attention. In bright sunlight, against wet mud or in the dripping rainforest canopy, metallic glints are surprisingly confusing to the eye of a predator, which searches for images based on shape.
Slimiest insect (#ulink_7a630d02-728c-5a23-bed4-c74755a902bc)
Contrary to popular opinion, insects (like snakes) are not slimy. Slime or, to give it its more technical term, mucus, is a sticky secretion used especially by molluscs and vertebrates. Snails and slugs use it to lubricate their path as they glide forwards on their own moist layer, and to a certain extent as a defence, since the stickiness deters predators, which can get gummed up in it. Vertebrates use it to line their airways, guts and genital tract, and to cover their eyes, where it forms a gel layer in which antiseptic enzymes can protect against microbial attack. Mucus is a very sticky substance, and very useful, so it will come as no surprise to learn that some insects use it after all.
Mucus is made up of mucin molecules – a number of long protein chains covered with atomic groups which resemble sugar molecules. The sugar parts (glycans) attract water (and each other) and as the long mucin molecules slide past one another, these areas act like weak glue, partly sticking the strands together. The mucus remains wet and tacky, and does not set hard like that other important long-chain protein molecule, silk, which is produced from the salivary glands of many insect larvae, which use it to spin a cocoon in which to become adult.
Fungus gnat larvae produce mucus from their salivary glands, but they do this throughout their larvahood, not just during metamorphosis at the end. The larvae of these small midge-like flies live under dead logs, fungal fruiting bodies or in caves. Here they build a rough sheet web of sticky mucus strands, covered all over in tiny water droplets. Sometimes they add a soft flexible tube into which they retreat for shelter. Many species eat highly nutritious fungal spores. The spores are impossible to catch when airborne but are caught in the gleaming mucus, and can then be eaten. The webs of some species also contain oxalic acid, a simple chemical similar to vinegar but much more powerful. It is highly toxic to many animals (including humans), and the gnat larvae use it to kill insect prey, which they then eat too.
Biggest blockhead (#ulink_87a9de49-e163-5c11-9aaf-090cc917206e)
Ants gain protection from a complex social hierarchy that generates workers to forage and build, and soldiers to fight and protect. The nest that they build and protect is the ants’ most important asset. Ants need to protect their nest from many enemies, including predators, parasites and other ants who would like to raid the valuable protein invested in the brood as well as any food stores laid up against hard times.
Soldier carpenter ants have evolved huge mallet-shaped heads with which to bar their nest entrances. Small holes are blocked by a single soldier, while for larger entrances several soldiers gather together to form a living barricade. The soldiers seldom leave the nest, but are fed by the workers that constantly come and go.
When a worker needs to exit or enter the nest (see opposite), it is recognised by the blocking soldier, which pulls back into the broader tunnel behind. It is thought a combination of the host nest’s chemical smells and the ‘right’ tactile signals from the worker’s antennae identify it as a fellow citizen. If there is an attack on the colony, alerted ants release a chemical called undecane from a gland in their abdomen. This creates rapid excitement of other ants, and the many soldiers rush to block all external and internal tunnels.
Most sexually dimorphic insect (#ulink_12b9a979-8f1b-5d7b-875a-92a0bc3538cd)
Males and females are different. Males produce huge amounts of tiny sperm, which they generally try to spread about between as many females as they can. Females carry the eggs, and although they may benefit from males competing for their attentions, multiple matings carry a cost in terms of time wasted and sometimes even physical damage. These different biological drives often produce very different behaviours in male and female of the same species, and sometimes also different body forms. In most insects these structural differences are small, but in one group of beetles, males and females are so different that they look like completely different organisms.
The European snail beetle, Drilus flavescens, is small (4 to 7 mm) and brown; it has a black head and thorax, and feathery antennae – at least the male has. The female, by extreme contrast, is a large, soft, flabby, caterpillar-like creature, 50 times as large as the male. The males fly on hot sunny days, but the females lack both the normal hard beetle wingcases and also the functional membranous flight wings. The distribution of the males shows that the species is fairly widespread on limestone or chalk soils, but despite this the female is virtually unknown. In fact, the female of this peculiar species is so rarely seen that there was no reliable published picture of her until this mating pair was photographed in 2003.
The larvae of Drilus eat small snails. Despite being a widespread insect, the rarity (or perhaps the secretiveness) of the females and larvae meant that the beetle’s life cycle was not worked out until 1903. Quite why males and females of Drilus should be so very different is still a bit of a mystery, although many female glow-worms (also beetles but in a completely different family) are also wingless, and their larvae, too, are snail predators.
Most mixed-up sexuality (#ulink_81f553ba-66bf-581b-8b3d-979e9410ddd6)
Insects are usually either wholly male or wholly female. In extremely rare situations, however, there appears an individual that is exactly half one sex and half the other – a bilateral gynandromorph – and nowhere is this more striking than when it involves a butterfly. In butterflies, as in most animals, sex is determined by the chromosomes. Females have two X chromosomes (XX) and males have just one (XO). Butterfly sperm contains either an X or no-sex chromosome.
In this marsh fritillary butterfly (Euphydryas aurinia) the sperm that originally fertilised the egg contained an X chromosome so the offspring was due to be XX, female. But after the very first cell division into two, one of the XX cells (female) somehow lost an X and became XO (male). Throughout the many millions of further cell divisions in the growing caterpillar and during metamorphosis in the chrysalis the right-hand side of the insect stayed female while the left-hand side had become male. When the final adult butterfly emerged from its pupa, it continued to be right half female and left half male.
Gynandromorphs are very rare and unlikely to survive. Neither male nor female sexual organs are functional. Some striking butterfly specimens occur where males and females have different wing patterns. In the case of the marsh fritillary, males are significantly smaller than females. This specimen was reared as part of a genetic study. In the wild all it could have achieved in life would have been a terminal spiral flight.
Most bloated insect (#ulink_fa328122-df35-5efb-ae71-aeb7bbfdb751)
For most aboriginal peoples, honey from bees was the only source of sweetness for thousands of years. But in Australia, western USA, Mexico, South Africa and New Guinea, they could raid another source – the hugely bloated honeypot ants.
Honeypot ants have grossly distended abdomens. Their job is to hang immobile from the roofs of nest burrows and fill up with the goodies brought back by their nest-mates, the workers – nectar and honeydew (aphid excrement little changed from the liquid plant sap these insects suck out). This behaviour has evolved in several different genera around the world, usually in desert habitats where the storage of food against hard times allows the colony to survive in the harshest of environments.
The storage ants, called ‘repletes’, can expand their bodies by a factor of many hundreds compared to the normal workers. Their translucent bodies vary in colour from almost clear, through yellow-brown to dark amber. The darker bodies contain the sugars glucose and fructose. The palest and heaviest repletes contain very dilute sugar solutions.
The evolution of repletes is thought to be linked to a system that exploits the unpredictable food sources provided by desert flowers. The volume of the repletes is built up in cool, moist weather, and they are then tapped by the rest of the colony during hot, dry times. The change from building up to tapping happens at about 30-31°C (86-88°F), suggesting that the real purpose of the repletes is to store water against drought.
Most seasonally dimorphic insect (#ulink_5f4a754e-263f-53a3-a416-5afcd9fdaf1d)
The European map butterfly, Araschnia levana, gets its name from the pretty patterns that mark the undersides of its wings. The mottled browns and oranges of its background are criss-crossed with bright white lines reminiscent of the radiating compass marks superimposed on old maps and nautical charts. However, it is the patterns of the upper sides that are most remarkable.
Spring butterflies, emerging from chrysalises that have remained dormant through winter, are bright orange above, marked with a series of black spots and blotches. Their eggs produce caterpillars that feed quickly on their nettle host-plants, and the summer generation of butterflies that emerges a few weeks later has a completely different colour pattern – jet black, with a strong white flash down each wing (shown right). So different are these colour forms that they were long thought to be two distinct species.
This extreme dimorphism (meaning ‘two forms’) has attracted a lot of research from entomologists, and the factors that decide which colour pattern will be produced are now well understood. The final adult morph is decided by the effects of day length and temperature on the feeding caterpillar. Short days and cold, enough to induce winter torpor, produce the spring orange form levana while long hot days produce the black and white summer form prorsa. Experiments have shown that caterpillars from either generation can be raised under artificially altered temperature and daylight regimes to produce the ‘wrong’ adults.
It is still not known why the map butterfly shows such stark changes between its two generations. The scene is further confused by the fact that more northerly and montane populations have only one generation (form levana) each year, while in the south there is a partial third generation with intermediate levana/prorsa characters.
As well as different colour patterns, the summer form prorsa has larger and less pointed wings, a heavier (presumably more muscular) thorax and relatively smaller abdomen. These characters fit the idea that the summer form is better at migrating to colonise new regions (the spring form is noticeably more sedentary), but it still does not explain why one butterfly species should look like two completely different creatures.
Highest number of wings (#ulink_192a5b38-0a9a-5097-a082-f9049a5da98d)
Adult insects usually have two pairs of wings. Some groups have fewer: flies have only one pair; lice and fleas have none at all. Even beetles, which might look as if they have none at first, still have four wings; two are developed into the hard shell wing-cases, and cover the delicately folded flight wings underneath. But could this be a moth with twenty wings?
Plume moths have long, narrow, hairy wings that resemble birds’ feathers. At rest they fold their wings up tightly to resemble twigs and dead grass stems. In some species the wings are split into hairy fingers, each finger acting as a structural vein to expand the narrow wings into a broader aerofoil in flight. The greatest splitting occurs in the twenty-plume moths, where each of the four ‘true’ wings is divided right down to the base into a fan of finger-wings. Whoever named the moth miscounted. In fact, it has 24 plumes.
The plumes of these moths are analogous to the veins that spread through all insect wings. The veins are most obvious in clear-winged insects such as bees, wasps and flies. Insect wings are thought to have evolved from broad flap-like appendages used as gills by their aquatic predecessors, and the veins are the vestiges of breathing tubes. Such gill flaps are still visible today in the larvae of stoneflies (Plecoptera) and mayflies (Ephemeroptera).
Insects are thought to have evolved wings only once, about 400 million years ago. After examining the different wing structures, scientists now believe that the first truly flapping and flying insects had eight veins in each wing. Over evolutionary time these have often become merged with each other or reduced to six main veins. These six archetypal veins are clearly seen in Alucita.
Flattest insect (#ulink_f9b959b2-e040-58f5-8d23-ac9b46e5995e)
Ground beetles (family Carabidae) are, as their name suggests, usually found running about on the ground, where they hunt small insects and other invertebrate prey. They are found throughout the world and are one of the most diverse and successful groups of insects. Their success is due in part to a peculiar structure near the base of each of their hind legs. The trochanter is a small muscle-filled lobe where the femur (thigh) joins the coxa (hip). It gives the long back legs extra strength, not just to push backwards, but to push downwards at the same time.
Ground beetles use this ability in a technique called wedge-pushing to squeeze into a tight space in the roots of grass or through the soil under a stone. First the beetle pushes its wedge-shaped body forwards as far as it can go, then it levers itself up and down to press back the herbage or soil slightly so it can push forwards again. Using this unique semi-subterranean propulsion method, ground beetles are able to pursue their prey farther and deeper into the dense thatch of plant roots and leaf litter.
The violin beetles – of which five species are known, all from Southeast Asia – have taken this squeezing habit to a bizarre conclusion. Rather than thrusting themselves through the undergrowth, they have chosen another, equally tight, spot in which to hunt: in the narrow crevices beneath the loose bark of dead trees, stumps and logs. As well as an extremely flattened body, violin beetles have a narrow head and thorax to examine minute cracks in the dead timber. They also explore cracks in the earth and the axils of bromeliads.
Most back-to-front insect (#ulink_78f880a1-7ecc-5c6f-9208-6eefabc46981)
Apple, pear and cherry leaves are prone to attack from the caterpillars of a tiny moth. The caterpillars are so small that rather than eat the leaves from the outside, they burrow along inside them, leaving a winding, pale, air-filled space behind. But what is most remarkable about this insect is that when the adult moth emerges it appears to have its head at the wrong end. Careful inspection of the moth’s tiny 4-mm wings shows that they are entirely white apart from the grey and black marks at their tips. The pattern of dark scales against white is clearly arranged to look like a separate miniature insect, with dark body outline, six legs, two short antennae and two round black eyes.
False eyes, heads and antennae are quite common in butterflies, with many species having prominent dark eye spots at the hind wing edges alongside short or long tails which resemble antennae. Swallowtails unsurprisingly have tails, as do many hairstreaks and blues. Lyonetia is one of a range of micromoths with false legs and heads at the tips of the wings. Some leafhopper bugs, which also have wings folded tent-like over the abdomen, have similar patterns.
Until recently, the conventional wisdom was that false heads attracted the attentions of predators to bite at the relatively expendable wing extremities, preventing fatal damage to the vital organs. However, an intriguing theory suggests that rather than attracting bites to the ‘wrong’ end, the false head at the tail encourages attack on the true head. A predator seeing the moth might reasonably feel its best chance is to sneak up from behind, but it will in reality be making a frontal advance on the insect’s real head, where it is more likely to be detected by the moth’s real eyes and real antennae.
Longest ovipositor (egg-laying tube) (#ulink_1afecbbb-7ee0-535f-944f-5127f21eaa15)
Ichneumons are related to wasps, but instead of building nests for their larvae, they choose a more insidious lifestyle for their young. Ichneumons lay their eggs in the bodies of other insects, usually moth and butterfly caterpillars, but also insect eggs or pupae. The hatching maggot then eats the host animal alive, from the inside, eventually killing it. An organism that lives on or in a host and kills it in this way is known as a parasitoid.
Together with the many other parasitic ‘wasps’, ichneumons are a large and diverse group of creatures, which target a huge range of insect hosts. At one end of the scale are some of the smallest insects known (see page 90); at the other end are the giant ichneumon or sabre wasps in the genus Rhyssa.
Giant ichneumons need a host animal of suitable size to feed their equally giant larvae, and choose the larvae of another group of very large insects – the horntails. Horntails (Syrex species) are huge hornet-sized insects, named after their own large, stout tails, which they use to saw into fallen logs and rotten tree trunks to deposit their eggs. Their large grubs will chew burrows through the dead wood for between one and three years before finally emerging as adults.
Rhyssa females are able to detect chemicals given off by the Syrex larva, even through 4 cm (1 ½ in) of wood. The narrow 4 cm tail of a sabre wasp, usually longer than the rest of her body, is composed of three pieces – two thick outer strips form a protective sheath that covers the needle-thin ovipositor (egg-laying tube). Using her long legs and flexible abdomen as a gantry, she slowly pushes the slim egg tube down through the timber until she is able to parasitise the grub below. Her offspring is now assured of food to see it through to adulthood, but the horntail maggot is doomed.
Widest head (#ulink_41fd84c0-9f1d-5b05-a8ba-a4f9d8d1e85f)
It is a sad fact of life that males often fight each other for the attentions of females. The prize for the victor may be a harem and numerous offspring, but the cost in energy expenditure and bodily damage may be high, and life expectancy short. It is better to be able to size up an opponent before falling to blows, and stalk-eyed flies do this eye-ball to eye-ball.
Many groups of small tropical flies have broad heads, and this is taken to extremes in the family Diopsidae. More than 150 species in this family have heads so wide that the eyes are held out on unfeasibly long, thin horizontal stalks. Very often the head width (12-14 mm) is twice the length of the fly’s body (6-7 mm). Head width, or rather eye-stalk length, is directly proportional to body size, and a good indicator of body strength, which itself is directly linked to the fly’s nutrition when it was a larva. Male diopsids face of fin a head-to-head stalk-measuring contest. The winner gets the females, but the loser walks away unharmed.
This ritual behaviour is thought to have evolved because these tropical flies are relatively long-lived (12 months has been recorded), and because they have something important to guard. Other groups of small flies with shorter lifespans and narrower (but still relatively stout) heads actually come to head-butting bouts: they have little to lose so they just go for it. Male diopsids, on the other hand, have been observed repeatedly contesting for 200 consecutive days.
The valuable resources that male diopsids are defending are string-thin rootlets hanging down from the banks of small streams that run through the woodland in which they live. These apparently mundane bits of straggling vegetation are the prime night-roosting sites for large numbers of females. They gather here and all face upwards, the direction from which any potential predator will come. By fighting, or at least flaunting his broad head, a male diopsid rules the roost and secures his harem.
Brightest light generation (#ulink_a5e5dff0-bfb4-5c03-9310-926d1f81e21e)
Several groups of insects can generate light, including the springtails, true bugs, fly larvae and especially the beetles. The well-known glow-worms and fireflies are neither worms nor flies, but beetles, and many species occur worldwide. Light-generating beetles use their lights to attract or communicate with potential mates. Some flash to a secret rhythm, while others emit a continuous pale glow. There has long been debate about which beetle species might be brightest and until recently comparisons were rather subjective, usually describing the similarity to a candle at some set distance as seen by the naked eye or to stars of various brightnesses. Supremely accurate photometers can now measure light production down to the atomic level, and a clear winner has been found – Pyrophorus noctilucus, a click beetle found in forests in the West Indies.
It is auspicious that this species should rank highest. In 1885 the French physiologist Raphael Dubois first isolated the compounds luciferin and luciferase by dissecting the glowing spots on the thorax of P. noctilucus. Similar chemicals are found in all light-emitting organisms. Light generation by living organisms (known as bioluminescence) is remarkable because it is ‘cold’. Using the old candle analogy, a firefly produces 1/80,000th of the heat that would be created by a candle of the same brightness.
The chemical reactions that produce light are based on the enzyme luciferase, which combines luciferin with oxygen and adenosine triphosphate (ATP). The significance of Dubois’s discovery was not fully understood for nearly 60 years until ATP was identified as the energy-carrying molecular currency in every living thing. In photosynthesis, light energy is captured by green plants and transformed into chemical energy in the form of ATP. This is used to make basic sugars and other substances from carbon dioxide in the atmosphere and water taken up by the roots. Photosynthesis absorbs light; bioluminescence releases light. The two reactions are equal, but the reverse of each other.
Most variable colour pattern (#ulink_7fe5a59e-33d6-5f4e-8e11-5af733d42e12)
Naming plants and animals should be a relatively straightforward procedure. Since the Swedish naturalist Karl von Linné (also Latinised to Carolus Linnaeus) developed the binomial (two-name) system, each organism has been given two names. Thus, for the seven-spot ladybird we have one name for the genus, Coccinella, meaning ladybird, and one for the particular species, septempunctata, meaning seven-spotted.
Except that nothing in nature is that straightforward. The common seven-spot always has seven spots, but the closely related ten-spot ladybird, Adalia decempunctata, very rarely has ten. In fact it can have anything down to no spots. It can be red with black flecks, black with yellow shoulder marks, chequered, netted, speckled or barred. When early naturalists put Linnaeus’s binomial system into use, they went to town with ladybirds.
There was sexmaculata and sexpunctata for six-spotted ones; octopunctata had eight spots, quadripunctata four; semicruciata was halfway to having a cross on its back; semifasciata had half a stripe; centromaculata had spots down the middle; triangularis had three marks; subpunctata had small spots; obscura was obscurely marked. There was only one small problem – all these were the same species.
There are over 80 different named forms of the ten-spot ladybird, many once thought to be separate species, but now recognised as one species featuring different genetically controlled colour patterns. Geneticists are still trying to work out how these patterns are controlled at the level of the genes and the DNA.
These are not races or subspecies, where particular colour-ways occur in discrete geographical zones or different places around the world. The different patterns often occur together, and in breeding experiments many different patterns can appear in the offspring of identical ‘normal’ ten-spotted parents.
One selection pressure that can drive the evolution of a diversity of forms is the presence of predators that hunt by favouring one precise colour-way. Birds, in particular, hunt using a ‘search-image’ in their brains, seeing targets that match the image but missing others that look slightly different. By having many different patterns, at least some individuals should survive to reproduce. The only trouble with this theory in this case is that all ladybirds are brightly coloured to remind birds not to eat any of them because they taste horrid. Quite why the ten-spot ladybird should have such versatile patterns is still open to debate.
Bloodiest insect (#ulink_bc984497-96ef-541c-b147-fcc584a02073)
Insects defend themselves from attack in many different ways. After hiding, possessing a weapon is one of the commonest strategies. The weapon may be biting or stinging an enemy, but it may also be simply tasting foul. Plenty of plants contain noxious chemicals to deter herbivores, and plant-feeding insects can take advantage of this fact by storing the poisons in their bodies.
There is one drawback for the individual with the poisonous body. Although birds (the main insect predators) may soon learn to avoid a particular species because it tastes disgusting, that is a bit late for the individual insect they have picked up, crushed, chewed and swallowed, even if they then vomit it back up again. It would be much better if the insect could warn of fits potential predator by giving it a taste of what might come should the meal be fully consumed.
This is exactly what many beetles do. Rather than wait until their innards are squashed out in the bird’s beak, they defensively squeeze out large droplets of their foul-tasting haemolymph (blood). As soon as the bird tastes the bitter chemicals, it spits out the not-so-tasty morsel more or less unharmed.
The commonest beetles to use this defence, called reflex bleeding, are ladybirds, which exude droplets of their yellow body fluids from special pores in their knee joints. The most spectacular, though, is the aptly named bloody-nosed beetle, Timarcha tenebricosa, which oozes out a great drop of bright-red liquor from its mouthparts.
Ladybirds are brightly coloured to emphasise the warning. Timarcha is a sombre black, but its colouring is equally obvious against the green of its meadow foodplants. This large, lumbering flightless leaf beetle has little to fear from predators and it feeds quite happily in broad daylight.
Most beautiful insect (#ulink_4c0c1bfc-480a-5819-8e0f-78896d64b99d)
Beauty is very much in the eye of the beholder; just look at some of the names cooked up by entomologists. Scientific names regularly include terms such as formosa (handsome), splendidissima (most splendid), pulchrina (beautiful), nobilis (noble), venustus (lovely) and elegans (elegant).
There are many insects worthy of the title ‘most beautiful’, but nowhere is this better described than in the words of Victorian naturalist, scientist and traveller Alfred Russel Wallace. In a time before research grants, Wallace financed his travels by making collections for wealthy patrons or selling the handsome and strange specimens when he returned home to Britain. The highest value specimens were fabulous birds of paradise and beautiful birdwing butterflies. He knew only too well the worth of his collections. On the morning of 6 August 1852, during his return across the Atlantic from South America, the ship on which he was travelling, the Helen, caught fire and sank. Wallace and the crew spent nine days in the open life boats before they were rescued, but all Wallace’s specimens were lost.
Undeterred, he published his Travels on the Amazon and Rio Negro and was soon off exploring and collecting in Southeast Asia. He managed to bring his booty home safely this time, and captured the essence of exploration, discovery and the hunt for fantastical beasts in Malay Archipelago, published in 1859. On his first venture into the forests of Batchian (now Bacan), one of the Mollucan islands of Indonesia, he caught sight of a spectacular birdwing butterfly. It took him a further two months to finally collect a specimen. Wallace later named it Ornithoptera croesus, after the 6th-centuryBCE king of Lydia (now part of Turkey) famed for his wealth. Wallace’s words still resonate today:
‘The beauty and brilliancy of this insect are indescribable, and none but a naturalist can understand the intense excitement I experienced when I at length captured it. On taking it out of my net and opening the glorious wings, my heart began to beat violently, the blood rushed to my head, and I felt much more like fainting than I have done when in apprehension of immediate death. I had a headache the rest of the day, so great was the excitement produced by what will appear to most people a very inadequate cause.’
Longest head (#ulink_ee766bcf-eb3b-5237-adac-0df253b8fbad)
It will come as no surprise to discover that some males have big heads. Big heads can be attached to big jaws (see page 60) or house big eyes (see page 56). But the male giraffe-necked weevil of Madagascar has the most awkward-looking head imaginable. And what does he use it for? Nodding.
The male’s long, slender head takes up about 10 of his 25 mm (1 in) length. The neck is another 7 mm, making the insect’s head and neck over 70 per cent of its entire body length. It holds them angled up from its squat body, like a miniature construction site crane. The female’s head and neck are also relatively long, but only about half her total body length.
The male uses his stretched form for no practical purpose. The nodding, however, is very important to other giraffe-necked weevils. It seems that the males contest one another, trying to out-nod their opponents in ritualised fights. After head-to-head nodding competitions, one male will retreat. It also appears that the females choose the best nodders with which to mate. Thus, over evolutionary time, the males with the longest heads (better for nodding) have been selected.
The irony is that it is the female who really needs a long head. Trachelophorus belongs to a group of beetles called leaf-rolling weevils. She chews through both sides of a leaf blade to the mid-rib. The leaf now has a tendency to curl, a property that she harnesses using her angled neck and head to roll the partly severed plant into a small cigar. She lays an egg inside, and the grub is protected from predators and parasites while it feeds.
Most streamlined insect (#ulink_8780aa0d-e16f-5379-a097-bb5f2d57a09b)
Despite rolling boulders and white water, life continues beneath the surface of fast-flowing rivers. There, attached to the stones in the water, live water pennies. So named because they are roughly the size of a one-cent coin (a penny), these creatures are the larvae of beetles. The adult beetles are terrestrial, but their larvae are wholly aquatic.
A water penny is multi-segmented, with each segment flattened into a flange that surrounds its body, hiding head, legs and gills beneath a smooth carapace. It clings tight to rocks and stones using its clawed feet. If it cannot get a purchase, then even slow-moving water can wash it away. The larvae spend most of the time under stones or pressed into small cracks in the rocks, feeding on microscopic algae. But they must leave the water to pupate, and at such times they are exposed to the force of the water.
In rapidly moving water, there is a boundary layer of calmer water at the bottom, slowed by friction with the river bed. Small and flattened, water pennies can sit within this layer, but they cannot afford to be complacent. As well as clinging on tight with their feet, they use hydrodynamics to hold fast. By pumping water out through the gaps between their segments and at the tail end of the body, they can reduce turbulence to creep slowly through the force of the flow.
Loudest insect (#ulink_ca859e81-b106-5a18-b3e4-cb7e40615fc5)
Insects are generally small, secretive and quiet. Most are reluctant to draw attention to themselves, but the cicadas are an exception. Along with crickets, katydids and grasshoppers, the cicadas use sound to communicate with each other, and they do so in the loudest manner possible.
On each side of the first abdominal segment is a large round organ called the tymbal. The tymbal, just like a drum, has a stiff elastic membrane held taught by a rigid circular frame. Inside the insect’s abdomen, a large muscle is attached by a narrow thread to the centre of the membrane. When the muscle contracts it distorts the tymbal membrane, causing it to buckle suddenly, creating an audible snap. When it relaxes, the membrane clicks back to its resting position. By vibrating the membrane at 4,000 to 7,000 times a second, the clicks become merged into a continuous whining buzz. Inside the abdomen, two air sacs (modified breathing tubes) are tuned to the natural frequency of the tymbals and act as amplifiers. The noise made is astounding, easily competing with loud power tools, lawn mowers or motorcycles. Cicadas on the motorway verge can often be heard from inside fast-moving cars, or through dense forest from over 1 km away.
The volume of a noise is measured using sound pressure level meters. The loudest sustained volume recorded for an insect is for an African cicada, Brevisana brevis, which clocked up 106.7 decibels. Human hearing is damaged by prolonged exposure to this volume and the recommended limit is less than two hours per day. Brevisana keeps it up all day long. The loudest peak cicada call ever recorded was for one of the North American dog day cicadas, Tibicen pronotalis, which reached 108.9 decibels during an alarm call. The normal purpose of cicada ‘songs’ is for males to call to females and announce territoriality to each other. On the whole the largest cicadas make the most noise, so everyone knows who is the biggest. Alarm calls are made as a defence against birds, and at these volumes the sound is truly repellent.
Best hoverer (#ulink_98655a39-a77a-55ec-a5f8-e91e34e6d65a)
When, on 29 September 1907, the French aviation pioneer Louis Charles Breguet lifted off the ground in an erratic prototype helicopter, Gyroplane 1, he was trying to emulate a flight technique long mastered by insects – hovering. The ability to hang in mid-air, even for just a moment, is of paramount importance if an insect wants to land on a leaf or a flower, as there are no runways for a glide-down descent.
Because insects can flex (twist) their wings, thrust and lift can be generated by both backwards and forwards strokes. In the fastest insects, the power stroke (pushing backwards) and the recovery stroke (pulling the wings forwards again) generate nearly all thrust, with just enough lift to keep level flight. In hoverers, thrust and lift are directed straight down, with just enough power to support an insect stationary.
Among the best-known hovering insects are the hawkmoths and bee-flies, which hover apparently motionless while drinking nectar from a flower. Others include the hoverflies, named for their habit of hovering in a shaft of light, over a flower, or in a woodland clearing. That hovering is important to these large and brightly coloured insects is demonstrated by the fact that they have huge eyes; in the males there is very little else on the head except the eyes. The large eyes give all-round vision to monitor the air-space in every direction and to maintain a fixed hovering point in the air. The males have larger eyes as it is they that do most of the hovering, guarding a three-dimensional territory, seeing off other males and enticing females.
But even hoverflies are out-hovered by one other group of insects, which are rather small and drab. The obviously named big-headed flies have big heads and, again, the males are all eyes. Their vast eyes give the same clue to all-round vision and territoriality. But instead of hovering brazenly in the large air-space under the spreading bough of a tree, they choose a discrete bush or a small space within the herbage. To the entomologist they demonstrate their flying skills by hovering in the folds of the insect net or inside the small glass tube as they are examined under a hand lens.
Ugliest insect (#ulink_d6721e7a-a4cf-51fd-a7d5-50071eb5a9c3)
It is the strange and unorthodox that most greatly offends our senses. This, combined with a lack of knowledge, creates fear and misunderstanding. So it is with the caterpillar of the lobster moth. And although derided as a gothic monstrosity and grotesque beast by many writers, it is not to offend or frighten humans that this strange and unorthodox maggot has evolved. Birds trying to eat it are its greatest enemies, and it is from them it must hide, or defend itself.
Early natural philosophers recorded that this peculiar animal was half spider and half scorpion. With its crustacean-like form, it is easy to see how it gets its English name. Its swollen tail has long, thin appendages, threateningly sting-like in appearance. These are the ‘anal claspers’, which in most other caterpillars are the last pair of sucker feet on the end of the caterpillar’s body. The second and third pair of front legs are also grossly lengthened and the caterpillar waves them about in an aggressive manner if disturbed.
Pretending to be dangerous is the last resort of the lobster moth caterpillar. It would rather remain motionless, undetected because it just does not look like an edible morsel. Its bizarre knobbly shape is likely to be overlooked by predators because instead of appearing like a ‘normal’ caterpillar (cylindrical, smooth, plump) it looks like a bit of shrivelled dead leaf.
The caterpillar does not always look so deformed. When it first emerges from its egg it resembles an ant, complete with long, skinny waist and round, bulbous abdomen. It can also exude formic acid, the same sharp-tasting chemical used by ants to dissuade birds from eating them. Incidentally, the word ‘lobster’, traced back through the Old English ‘lopustre’ and Anglo-Saxon ‘loppestre’ or ‘lopystr’, comes from a corruption of the Latin ‘locusta’ – perhaps an even uglier beast if its habits are taken into account.
Largest jaws (#ulink_b640d6c8-e32a-5475-bcba-30526391b315)
The most obvious purpose of jaws is eating. But this is really a secondary use, because plenty of insects eat without the aid of jaws. There is an even more basic function – biting. An insect may bite to catch and kill prey, to manipulate soil or cut leaf particles, or to chew a burrow into wood. Each of these behaviours requires its own type of jaws. And the insect with the most remarkable jaws uses them for a most remarkable behaviour.
Grant’s stag beetle, Chiasognathus granti, is sometimes also called Darwin’s stag beetle because he pondered on it in his famous book The Descent of Man
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