Extreme Insects. Richard Jones

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

NAME	apple leaf-miner moth Lyonetia clerkella
LOCATION	Western Europe
ATTRIBUTE	appears to have legs, eyes and antennae at the tips of its wings

      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)

NAME	sabre ichneumon in the genus Rhyssa
LOCATION	Europe, North Africa, Asia, North America
ATTRIBUTE	hypodermic-like egg-laying tube longer than the rest of its body

      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

NAME	stalk-eyed flies in the family Diopsidae
LOCATION	throughout the tropics, particularly Southeast Asia and Southern Africa
ATTRIBUTE	eyes on thin stalks longer than their bodies

      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