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 INSECTS ENTOMOPHAGA Ichneumons and their Allies This group comprises several thousands of species, of which, though some are of moderate size, the great majority are very small .and obscure, and in the present imperfect state of our knowledge the study of most of them is attended with considerable difficulty ; for while many are excessively variable, others though abundantly distinct are superficially so much alike, and their specific distinctions are so minute and so easily overlooked, that only a very few experts are able to deter- mine them with certainty. They are divided into several sections, which include the Cbrysididte, the Icbneumonidcf, the Braconida, the E-vaniidee, the Chalcidida and the Proctotrupida. As a rule they are parasitic upon other insects, a large proportion of them passing their earlier stages in the larva? of the Lepi- doptera. The Chrysididce or Ruby-tailed flies are not very numerous in Britain, and their proper place is perhaps rather with the Aculeata than the Entomophaga. They prey upon certain of the bees and wasps, laying their eggs in the burrows of their victims after the manner of the cuckoo bees. They are extremely beautiful insects, being resplendent with brilliant blue, green, crimson, burnished copper and other gorgeous colours. The Ichneumonidce, Eraconidce and E-vaniida deposit their eggs principally upon or in the larva? and ova of the Lepidoptera, but they attack other insects and also spiders ; and upon the efficient discharge of their important functions the welfare of the world depends to a far greater extent than the world generally is at present aware of. For if all insects were allowed to increase without let or hindrance, they would multiply at such a prodigious rate that every green leaf would speedily be devoured by them. It is quite true that other agencies, such as insectivorous birds, are also at work in keeping them in check, but it is probably not going too far to say that the birds are but the Sauls who slay their thousands while the ichneumons are the Davids who slay their tens of thousands. Nay, it is highly probable that by far the larger portion of those larva? which are consumed by birds would perish in any case from the attacks of ichneumons, and more than possible that in many instances the attacks of birds, though immediately fatal to multi- tudes of individual larvae, may be ultimately beneficial to the species to which they belong by the wholesale destruction of its far more inveterate and insidious foes. But while of the innumerable larva? that emerge from the egg very few escape from the attacks of the ichneumon, Nature is also careful of her children in more ways than one ; for when a parasite becomes so numerous as to threaten the extinction of a race, it is very frequently itself preyed upon by a hyper-parasite, which attacks it after a similar fashion. The Chalcididee are for the most part extremely minute brilliantly coloured insects, with habits similar to those of the Ichneumonidcc. The in