True insectsInsects have a head with one pair of antennae and three pairs of mouth-parts; a three-segmented thorax with a pair of legs on each segment and usually a pair of wings on each of the two rear segments; and a legless abdomen of 11 segments. There are 29 orders.
Mayflies; 1300 species
Mayflies are fragile insects, usually with four membranous wings, held vertically over the body when at rest; the hind wings are small and may be absent. The aquatic larval stage with gills may last three years before the first adult stage is reached. Then after a few hours, the skin is shed and the fully functional adult with stronger wings and more lustrous colour appears - only to die one day later.
Dragonflies and damselflies: 4500 species
The members of this order are strong fliers with a long narrow abdomen, very short antennae, huge eyes and legs set well forward to catch the smaller insects they prey on. The well-developed lower lip of the aquatic larva covers the face like a mask, and can be unfolded rapidly to seize small aquatic animals. There are two main sub-orders - the Anisoptera, the dragonflies, which rest with their wings spreadout; and the Zygoptera, the more delicate damselflies, which rest with their wings folded back.
Notopterans: 6 species
These wingless insects, living in the cold mountains of North America, Japan and Siberia, show a combination of features found in other orders. The insects with which they share characteristics include crickets and earwigs.
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Stoneflies: 1300 species
The weak-flying stoneflies, like the mayflies and dragonflies, have aquatic larvae. They are soft-bodied, rather flat insects with a broad head, long antennae and clear wings.
Web-spinners: 150 species
These fragile insects live in silken tunnels under stones, especially in the tropics. The first segments of the forelimbs are expanded and carry silk glands. The female is wingless.
Cockroaches: 3500 species
Cockroaches have long antennae, short cigar-shaped bodies, and thick leathery forewings which protect the hind wings.When at rest, the wings are folded back and lie on the abdomen.
Mantids: 1800 species
These insects sit motionless as if praying, then quickly grasp an insect, impaling it on the sharp spines of their front legs. The female eats the male after mating has taken place.
Termites: 1900 species
Termites are near-relatives of cockroacges but differ from the in having two small pairs of fragile wings which are shed after a brief courtship flight, and before mating. The mated pairs found colonies, which may vary in numbers from a hundred to hundreds of thousands of termites living in elaborate nests, or in galleries built in wood or soil. Termites have a highly developed social orginisation based on many castes. The female, or queen, fertilised at intervals by the king, becomes ditended, like a soft white sausage. The workers - small, wingless, sterile offspring - construct the nest, care for the eggs and find food. Sterile and wingless soldiers, often with big heads and jaws, defend the colony. Colonies may last up to 100 years.
Zorapterans: 16 species
These minute insects, less than 0.5cm long, are related to the book-lice. They live under bark in decaying woodand in humus in West Africa, Ceylon, Java, Texas, Florida and Bolivia.
Grasshoppers,crickets and allies: 10 000 species
Most of the Orthoptera have long hind legs with powerful thighs enabling them to make long jumps. They make noises by rubbing hard parts of the body together and they have hearing organs. Leathery forewings protect the fan-like hind wings. Locusts, which swarm in huge numbers and destroy vegetation, are members of this order.
Stick-insects and leaf-insects: 2000 species
The bodies of these predominantly tropical insects are either thin and twig-like, or flattened like leaves. They remain motionless by day, disguised by their resemblance to plants, and feed and move at night. Their eggs, which are large and hard-shelled, resemble seeds.
Earwigs: 900 species
These insects have horny forceps, forceps, used in defence. Short leathery forewings protect the delicate semicircular hind wings, which are pleated like a fan.
Book-lice: 1000 species
These tiny, soft-bodied insects with long antennae are found on trees or under bark and stones. Some are wingless.
Bird-lice: 2600 species
These tiny, wingless, rather flat insects with small eyes live as parasites on birds and small mammals. They feed on feathers and skin, and some drink blood.
Sucking-lice: 250 species
These parasites on mammals have mouth parts which are adapted for biting or piercing the skin for blood.
Thrips: 5000 species
These small, slender-bodied insects, common on flower-heads, especially dandelions, have peircing mouth-parts and tiny narrow wings fringed with hairs.
Bugs: 55 000 species
All the members of this diverse order have mouth parts in the form of a beak, with the jaws transformed into thread-like stylets capable of piercing and sucking. The forewings have a thickened membranous section which overlaps the abdomen when the wings are at rest. The sub-order Heteroptera includes bed-bugs, waterboatmen and water scorpions. The sub-order Homoptera includes cicadas and aphids.
Lacewings and ant-lions: 4000 species
These insects, which vary greatly in size, are usually predatory. The adults have biting mouth parts ans gauzy, net-like wings which form a roof over the abdomen when at rest. Their larvae are predatory.
Alderflies: 500 species
These insects are commonly found on vegetation near water. Their larvae are aquatic, with gills on the abdominal segments.
Snakeflies: 80 species
This group is found in all continents except Australia. Most species have unusual neck-like extensions of the thorax and the female lays eggs under bark, particularly of conifers, through a long needle-like ovipositor.
Beetles: 300 000 species
About 30-40 per cent of all insects are beetles. They vary greatly in size and structure, but can be easily recognised because their forewings are modified into horny sheaths completely concealing the hind wings when the insect is not flying. Their sizes range from 0.075cm to 15cm long, and the heavily built Goliath beetle Goliathus giganticus is 8 million times heavier than the smallest species. Beetles live in water or on land, and some burrow in the soil. Their larvae vary from legless grubs to caterpillar-like forms preying on other insects.
Strepsipterans: 300 species
The larvae of these insects are parasites in bugs, ants, bees and wasps. The adult female, which is little more than a sack of eggs, never leaves the host. The male is winged and free-living, but has only hind wings, the forewings being represented by balancing organs which are important in regulating stable flight.
Scorpionflies: 300 species
The elongated heads of these insects point downwards. The male has prominant reproductive organs contained in the last segment of the abdomen, which curl up over the back like a scorpions tail.
Caddisflies: 3500 species
These weak-flying flies are moth-like in appearance, but their wings are hairy not scaly. Their mouth-parts are adapted for licking fluids but many do not feed at all as adults. The aquatic larvae, sometimes called caddis worms, build and live in protective cases made of secretedsilk, stones, leaves or shells.
Zeuglopterans: 100 species
These small moth-like insects are found in large numbers on flowers such as buttercups in spring. They feed on pollen.
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Butterflies and moths: 120 000 species
Six of the 80 families of this large group consist of brightly coloured, day-active butterflies, most of which fold their wings vertically; the rest are moths, which fold their wings horizontally and are mostly nocturnal. All members of the order have two pairs of wings covered with powdery scales and a long sucking proboscis formed from one pair of mouth-parts. This is coiled when not in use.
True flies: 75 000 species
The true flies have only one pair of functional wings, the hind pair being reduced to a pair of knobs used to maintain balance. One group includes the slender bodied midges, craneflies (known as daddy long-legs in Britain) and mosquitoes. Another contains the blood sucking horse-flies and clegs, and a third, the compactly built houseflies, bluebottles, hoverflies and fruitflies with mouths adapted for sucking fluids. The soft, plump-bodied larvae, called maggots, usually feed on decaying matter or dung.
Fleas: 1800 species
Adult fleas are parasites on birds and mammals. They are brown, wingless insects with bristly vertically compressed bodies. The mouth-parts are modified for piercing and sucking, and in many species the well-developed hind legs are used for jumping.
Ants, bees and wasps: 100 000 species
Members of this group have two pairs of glossy, membranous wings, and the forewings are linked to the hind wings. The mouth parts are primarily adapted for biting, and often for lapping and sucking as well. There are two sub-orders. The Symphyta includes the saw-flies and the wood wasps, which insert their eggs into plants and have no obvious 'wasp waist' between the thorax and abdomen. The Apocrita includes the parasitic gall wasps, which lay their eggs in plants; ichneumon flies, which lay their eggs in the larvae or eggs of other insect; and the free-living bees, wasps and ants, which have a noticeable waist and seek food for their larvae. Many of these live in complex societes
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