Insects
20th September 2000 Back to Home Page Beetles Butterflies Dragonflies Hoppers
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One end of the delicately sculptured egg splits five ways, and five pointed petals curve back. A head appears, a head with a pale translucent appearance, a head with two bright red eyes. Slowly, the animal emerges from the shell, and extends six legs, two of which are long and feathery. It gathers itself together, and starts to swim. It is the minute larva of a water-boatman. One day it will be an insect which can fly and swim. If you have witnessed the transformation of a caterpillar or a large beetle larva into a pupa, if you have seen a crumpled moth or butterfly emerge painfully slowly from the pupal case and slowly transform into a beautiful creature, if you have seen a dragonfly dragging itself out of the larval skin and become a brilliant flyer, then you have witnessed something that is exceedingly common, but miraculous none the less. No matter that there are millions of species, and trillions of individuals. No matter that such things have been happening for tens of millions of years: it's hard to remain unmoved, and hard to forget. And what a strange transformation goes on inside the mysterious pupa, almost as if the larva dissolves into a formless fluid, from which gradually appears a perfect insect. The original morphing. |
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insects have six legs, though in a few cases, such as the Nymphalid
butterflies, one pair has degenerated, During tens of millions of
years, the insects have not shown signs of acquiring a fourth pair of
legs.
This apparent rigidity is typical of many taxa. A group evolves comparatively rapidly, and then settles down into a long phase during which multiple genera and species emerge, while retaining most of the typical features. But within the constraints of being insects, these animals exhibit enormous diversity of forms and habits. The great division is between the Apterygota, with no wings, and the Pterygota, which generally have wings. The Pterygota are themselves split into two divisions. One comprises the Exopterygota, in which the wings develop externally, and the young resemble the adults in many ways. The other comprises the Endopterygota, in which the wings develop internally, and there is metamorphosis between young and adult. The young of many insects very often occupy different habitats from htose of the adults. |
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Insects are classified into many
different orders, which are groups which are believed to have common
ancestry. Within these are families with closer relationships and genera
which are even more closely related.
The classification of any group of organisms is unlikely to be universally agreed, because knowledge is never complete, and in the case of fossils, more incomplete than complete. Only the most durable parts of an organism are likely to form a fossil - this eliminates many characteristics that would help to classify living things. The insect depicted at left, on a fuschia flower, is an aphid, a sap-sucking insect in the order hemiptera, sub-order homoptera. Parthenogenetic wingless generations in spring can build up numbers rapidly. Later generations may be winged, and eventually both sexes are produced. Aphids may be looked after by ants, who need their secretions. Aphids are preyed upon by both immature and mature ladybird beetles, but they can be serious pests. |
The classification of insects in these isles is something like this -
Phylum Arthropoda -
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Crustaceans Myriapods Arachnids Insects |
crabs, shimps, woodlice, etc centipedes and millipedes spiders, mites, scorpions, etc flies, butterflies, beetles, etc |
several pairs of legs many legs usually eight legs usually six legs |
Class Insecta
| Apterygota - Primitive wingless insects. Primitive they may be, but they are still here. |
| Thysanura
Diplura Protura Collembola |
silver-fish
springtails |
| Exopterygota - Wings develop externally, and the young vaguely resemble the adults. |
Ephemeroptera Odonata Plecoptera Orthoptera Dermaptera Dictyoptera Psocoptera Mallophaga Anoplura Hemiptera Thysanoptera |
mayflies damselflies and dragonflies stoneflies crickets and grasshoppers earwigs cockroaches booklice biting lice sucking lice bugs thrips |
| Endopterygota - The wings develop inside. There is metamorphosis - the young are unlike the adults. |
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Neuroptera Mecoptera Lepidoptera Trichoptera Diptera Siphonaptera Hymenoptera Coleoptera Strepsiptera |
alder flies, snake flies and lacewing flies scorpion flies butterflies and moths caddis flies flies fleas bees, wasps and ants beetles bee parasites |
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Ptera refers to wings. Aptera means without wings. The words "fly" and "bug" are often used in a very general sense, but they are also used in the limited sense of Diptera and Hemiptera. Lepidoptera means "scaly wings". The picture below shows some of the scales on the wing of a Small Tortoiseshell butterfly, Aglais urticae. |
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