150 



witli Lvcilia cacsar, with similar results, all the larvae of the 

 latter fly being- very soon destroyed by those of the former. The 

 larvae of //. deniipes become predaceous only npon reachino- their 

 third stage, and their method of destroying- other larvae is 

 described in detail, as well as an experiment which showed that 

 the disappearance of the honse-fly maggots was directly dne to 

 those of Hydrotaea. 



The author further describes experiments on the relations be- 

 tween the larvae of //. dentipes and those of Polyetes alholineata, 

 which are the most rapacious of all coprophagous larvae. Some 

 of the latter having been placed on some horse-dung in which the 

 larvae of //. dentipes had already destroyed a great many house- 

 fly maggots, immediately attacked these victors and quickly 

 killed and ate them. The resistance of the larvae of H. dentipes 

 was usually fierce and persistent, but never successful. 



Larvae of H. denti2:)es were never seen to attack each other, 

 even when other food was scarce, while such cannibalism is often 

 practised by the larvae of Myospila ineditahunda and Polyetes 

 alholineata. 



The importance of H. dentipes as destroyers of the larvae of 

 M. doniestica and of S. calcitrans is very great; and they also 

 present the following advantageous characteristics : they are very 

 fertile, laying 170-200 eggs, maturing at about the same time; 

 their larvae can travel very rapidly, and whether living in large 

 companies, or singly (when grown up), never eat each other, 

 even when hungry; the larvae are omnivorous feeders and will 

 live on all materials serving as breeding places for the larvae 

 of M. domestica ; the flies do not trouble men and never visit 

 human dwellings; and they can be readily reared in captivity. 



Reference is made to a statement bv Howard (" House Flies," 

 Farmers' Bull. 459, Washington, 1911, p. 12) that in Wash- 

 ington, the heaps of horse-dung brought out daily from the 

 stables of the Department of Agriculture, where 12 horses were 

 kept, were swarming with the larvae of M. domestica, and the 

 author suggests experimenting on these heaps with the larvae 

 of H. dentipes. He describes his observations in a " fairly 

 dirty " stable in the district of Tsarskoie Selo where he found 

 no larvae of M. domestica or *S'. calcitrans , or only very few of 

 the former, while the larvae of H. dentipes were always abundant. 

 In his opinion, H. dentipes (in addition to other parasitic insects) 

 is chiefly instrumental in preventing the multiplication of M. 

 domestica, which otherwise, under the protection of man, would 

 make human life intolerable. 



The larvae of H. dentipes were seldom found in the open, nor 

 in the large heaps of horse-dung in fields or woods, where they 

 would have been destroyed by Polyetes alholineata; similarly 

 they could not survive in human excrement in the open, as this 

 is always inhabited by larvae of Myospila meditahunda and other 

 flies. The eggs and larvae of this fly are safer in the dead bodies 

 of animals in the open, as there they can feed on the larvae of 

 Lucilia caesar. The flies of //. dentipes are found in woods, 

 fields and gardens, not far from human habitations; their usual 

 abode is the neighbourhood of stables. In size and form their 

 eggs are yery similar to those of Musca domestica, though a 



