THE CLUSTER FLY 239 



animal and vegetable matter. Macquart, also speaking 

 of the genus and not especially of this species, states 

 that the larvae develop in the manure pile and cow 

 droppings. The only definite recorded observation 

 which seems to have been made upon the actual breed- 

 ing habits of this species, in fact, is the rearing of a 

 single specimen from cow dung. This single specimen 

 was reared in the Insectary of the Bureau of Entomol- 

 ogy December 23, 1899. The writer has, however, 

 received a letter from Prof. J. S. Hine, of the Ohio 

 State University, in which he states that during the 

 summer of 1910 he reared numbers of cluster flies, to- 

 gether with other dipterous insects from accidental cow 

 droppings in the pasture.* 



In the absence of further exact observations, it is 

 fair to suppose that the cluster fly breeds in decompos- 

 ing animal matter of some kind or other, and it is alto- 

 gether likely that measures taken against the breeding 

 places of the true Musca domestica will also be meas- 

 urably effective against this species. There is as yet, 

 however, the possibility that it may breed in rich soil 

 or decomposing vegetable substances. It is difficult to 

 keep out of the house by screening, but it may be killed 

 by a light kerosene spray or by the free use of a fresh 

 pyrethrum powder. 



Marlatt (Insect Life, Vol. IV, 1891) records an ex- 

 traordinary mortality among these flies which he no- 

 ticed on the grounds of the Department of Agriculture 

 in the autumn of that year. He found often as many 

 as eight or ten flies fastened by a fungous growth to 



*D. Keilin (C. R. Soc. de Biologic, Vol. 67, p. 201) states that 

 the larvae of Pollenia are parasitic in certain earth-worms. 



