Insect, the anglicized form of the Late Lat. insectum, used by Pliny in his Natural History as the equivalent of the Gr. ἔντομον. Aristotle had included in one class “Entoma” the six-legged arthropods which form the modern zoological class of the Hexapoda or Insecta, besides the Arachnida, the centipedes and the millipedes. The word was introduced to English readers in a translation (1601) of Pliny’s Natural History by Philemon Holland, who defined “insects” as “little vermine or smal creatures which have (as it were) a cut or division betwene their heads and bodies, as pismires, flies, grashoppers, under which are comprehended earthworms, caterpilers, &c.” Few zoological terms have been more loosely used both by scientific and popular writers. The definition just quoted might include all animals belonging to the groups of the Arthropoda and Annelida, and U. Aldrovandi in De animalibus insectis (1602) almost contemporaneously distinguished between “terrestrial insects,” including woodlice, earthworms and slugs, and “aquatic insects,” comprising annelids and starfishes. Perhaps the widest meaning ever attached to the word was that of R.A.F. de Réaumur, who “would willingly refer to the class of insects all animals whose form would not allow them to be placed in the class of ordinary quadrupeds, in that of birds, or in that of fishes. The size of an animal should not suffice to exclude it from the number of insects.... A crocodile would be a terrible insect; I should have no difficulty, however, in giving it that name. All reptiles belong to the class of insects, for the same reasons that earthworms belong to it.”
The class Insecta of Linnaeus (1758) was co-extensive with the Arthropoda of modern zoologists. The general practice for many years past among naturalists has been to restrict the terms “Insecta” and “insect” to the class of Arthropods with three pairs of legs in the adult condition: bees, flies, moths, bugs, grasshoppers, springtails are “insects,” but not spiders, centipedes nor crabs, far less earthworms, and still less slugs, starfishes or coral polyps.
For a general account of the structure, development and relationships of insects, see Arthropoda and Hexapoda, while details of the form, habits and classification of insects will be found in articles on the various orders or groups of orders (Aptera, Coleoptera, Dipteria, Hemiptera, Hymenoptera, Lepidoptera, Neuroptera, Orthoptera, Thysanoptera), and in special articles on the more familiar divisions (Ant, Bee, Dragon-fly, Earwig, &c.). The history of the study of insects is sketched under Entomology.
