216 INSECT TRANSFORMATION 



those of the larva, and herein lies its danger to man, its 

 unwilling host. A house in which house-flies could find suitable 

 breeding material would be an exceptionally dirty place, but 

 these insects often come straight from the unspeakable filth 

 in which they lay their eggs, to walk over butter or fall into 

 uncovered milk- jugs. Thus typhoid and infantile diarrhoea 

 are spread, and it is realized how important for the health and 

 welfare of human societies may be a knowledge of the surround- 

 ings amid which common insects and their larvae live. 



While decaying plant-tissues, refuse and excrement furnish 

 thus a rich food supply for diverse insect larvae, many others 

 live in the bodies of dead animals. In the Silphidae or carrion- 

 beetles, we see a family of insects in which the carrion-feeding 

 habit is prevalent both among adults and larvae. The well- 

 armoured woodlouse-like grubs of species of Silpha (Fig. 58) 

 wander about in search of dead animals on which they may 

 feed, though some of them seek other sources of nourishment, 

 such as live snails which they hunt and devour. The well- 

 known burying-beetles (Necrophoms) work in companies, 

 interring the bodies of small beasts and birds, on which they 

 lay their eggs so that the larvae, when hatched, find themselves 

 close to a large mass of suitable food. In correspondence 

 with their quiescent mode of life these Necrophorus grubs 

 differ from the armoured Silpha larvae, having a softer cuticle 

 beset with spiny plates. Turning to the Diptera, it may be 

 noticed that some of the most abundant and familiar of insects, 

 such as the blue-bottles (Calliphora) the green-bottles (Lit cilia), 

 and the large, grey flesh-fly (Sarcophaga), lay their eggs (the 

 notorious " fly-blow ") on flesh, into which the maggots, with 

 their strong, sharp mouth-hooks, quickly eat their way. On 

 this highly nutritious food they gnfVv fast, and pass rapidly 

 through the successive stages of the life-history, so that the 

 flies of a second generation may appear in a fortnight. 



Many cases are on record of blue-bottle maggots feeding on 

 or in the bodies of living animals instead of in dead flesh. 

 This horrible habit on the part of the larvae is a sequence to 

 the act of the female fly in laying her eggs on a live instead 

 of a dead animal, and it has been observed that neglected 

 sores or wounds prove especially attractive to the flies, which 

 on occasion make use of human beings for egg-laying. In 



