Extreme Insects

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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