Insects are by far the most numerous class of animals : about eleven thousand species have been described by Gmelin, in the last edition of the "System of Na ture :" a great many more have been de scribed by other naturalists since the pub lication of that work ; and a very consi derable number are to be met with in the cabinets of the curious, which have not as yet been described by any author. In those parts of the world which we are best acquainted with, we may easily sup pose that many species of insects exist, which have hitherto escaped notice. The minuteness of some insects makes them easily overlooked ; the agility of others renders the catching of them difficult ; the retired situations which many of them haunt favour their concealment. In the unexplored parts of America, Africa, and Asia, many thousand species must exist utterly unknown to naturalists : all these circumstances render it very probable, that not one half of the insects which ex ist in the world have hitherto been de scribed. In order to exhibit the propor tion they bear to plants,it may be proper to remark, that, as inhabitants of England, eight thousand species have been already described, and only three thousand plants.
Insects afford nourishment to a great number of the superior animals : many of the fishes, reptiles, and birds, draw the principal part of their sustenance from that source. The immense swarms of dif ferent species of crab, which abound in every sea, directly or indirectly form the principal part of the food of the cod, had dock, herring, and a great variety of fishes. The snake, lizard, frog, and many other reptiles, feed both on land and aqua tic insects. Gallinaceous fowls, and many of the small birds, &c. feed on insects. Swallows, indeed, feed entirely on wing ed insects. They afford food, likewise, to many of the mammalia, viz. to many species of the bat, to the ant-eater, &c. and even to man himself. Many species of crab, viz. lobster, common crab, shrimp, prawn, land-crab, &c. are reckoned deli cacies. The larva of some coleopterous insects and locusts form part of the food of man. Insects, likewise, by consuming decayed animal and vegetable matter, which, if left to undergo the putrefactive process on the surface of the ground, might taint the atmosphere with pestilen tial vapours, preserve the air pure for the respiration of man and other animals.