Extreme Insects. Richard Jones

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СКАЧАТЬ id="ulink_e71297a5-c1bf-56ed-b6cd-283ff2ef21c8"> Shiniest insect

NAME	golden chafers in the genus Plusiotis
LOCATION	Central and South America
ATTRIBUTE	appear to be wrought from burnished gold and silver

      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

NAME	fungus gnat larvae in the family Keroplatidae
LOCATION	worldwide
ATTRIBUTE	create mucus webs to collect their food

      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

NAME	carpenter ants Colobopsis truncatus (and other species)
LOCATION	worldwide
ABILITY	uses its head as a living gate at the entrance to its burrow

      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

NAME	European snail beetle Drilus flavescens
LOCATION	mainland Europe and the UK
ATTRIBUTE	most extreme difference between male and female

      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 СКАЧАТЬ