"In this manner all the slender-bodied tribe behave, differing only in some particular circumstances; as, for instance, the largest Libellas, as that at Fig. 5. Pl. 47. are not near so long in copulating or wooing as the small ones; for by the former this act is performed in a very short space, and while they are flying about in the air. Others, of a smaller size, are less quick in this performance; and as we descend to the smallest species, we shall find they take by much the longest time; observing, by the way, that all these slender-bodied ones lay their eggs in the same manner, that is, by fixing them to some substance to which they adhere, till they are ripened into life. My experience well informing me they never scatter them in any loose careless manner as some insects do, but are placed in such proper and apt situations as to receive the influence of the sun to bring them to maturity. "If we attentively consider these creatures, either in their caterpillar or complete states, we cannot help concluding them to be a rank of beings of greater benefit and advantage to mankind than they appear to be at first view; for, not to mention their being annual 'ministers of nature,' they are appointed by the great Governor of the universe as grand instruments for assisting to preserve that equilibrium so apparently reigning through the insect world, and which all who have made any progress in the study of natural history unanimously confess. Hence the voracious disposition of the Libellas is wisely made to answer a most necessary and beneficial purpose; and the great numbers of small insects which are daily sacrificed to their insatiable appetites, both in their caterpillar as well as complete states, is as strong an instance as any I know of the necessity and propriety of the existence of these animals. The general principle reigning through the whole animal kingdom, of the stronger preying upon the weak and defenceless, can hardly be explained to the purpose of being useful to mankind, and agreeable to the laws of nature, in any one instance more than is evidently to be observed in the subjects I have been describing. The least reflection will confirm this; for if the food of the Libellas when in their complete forms had consisted of the leaves of plants, like the locust genus, and not of those small insects they now prey on; or had it, like the beetle tribe, consisted of the superfluous parts of nature, as the putrid carcases of dead animals, rotten wood, &c. how great a chasm would there have been in the universal chain? how evident and conspicuous would it have appeared? and how could the vast number of small insects, increasing every day during the summer, be restrained and lessened? what genus of the transparent-winged class could possibly have performed this business singly? or could all the genera of flies, and even birds that we know of, have accomplished this end? could all the Dipteræ, or any other {116}kinds