Extreme Insects. Richard Jones

Most bloated insect

NAME	honeypot ants Myrmecocystus species, Camponotus inflatus and others
LOCATION	Australia, New Guinea, South Africa, western USA to Mexico
ABI LITY	use their stretched bodies to store sugar and water

      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

NAME	map butterfly Araschnia levana
LOCATION	widespread across mainland Europe
ATTRIBUTE	alternating generations of completely different-looking butterflies

      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

NAME	twenty-plumed moths in the genus Alucita
LOCATION	worldwide
ATTRIBUTE	more wings than any other insects

      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

NAME	violin beetles in the genus Mormolyce
LOCATION	Southeast Asia
ATTRIBUTE	most flattened insect form

      Ground beetles (family Carabidae) are, as their name suggests, usually found running about on the ground, where