Introduction to invertebrates

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Invertebrates – animals without a backbone – form more than 70% of all known species on the planet, and around 97% of all animal species. Insects, in turn, form the vast majority of invertebrates and, along with plants, are the dominant species on land in terms of numbers.

Without insects many higher forms of animal life would not survive. Most birds, for example, are insectivorous, and an average brood of great tit chicks will eat tens of thousands of caterpillars before leaving the nest. And, of course, many plants depend on pollination by insects to reproduce.

Most insects are so small and/or so inconspicuous that only an entomologist or an enthusiastic amateur naturalist is likely to notice them, and here we concentrate on the small minority of larger, more noticeable insects. These include some of the most attractive and spectacular of all animals, such as for example the peacock butterfly, the banded demoiselle damselfly, or the stag beetle. As well as butterflies, dragonflies and some beetles, we cover day-flying moths (a tiny minority among the moths as a whole);bees and wasps, which play an important ecological role; grasshoppers and crickets, heard more often than they are seen; and the flies, including in particular the hoverflies, probably the most spectacular of the flies, and also the most beneficial to man.

After the insects, arachnids – spiders and their allies, such as scorpions – form the largest group of invertebrates. They (the adults, anyway) have eight legs to the insects' six, and most of them are predators or parasites of insects.