97 



exists in sufficient quantity through the pastures to harbor the multi- 

 tudes of flies which are constantly issuing through the summer. How- 

 ever, many living females were captured and placed in breeding cages 

 with horse-dung and decaying animal and vegetable material of differ- 

 ent kinds, each isolated, and it resulted that a few oviposited in the 

 horse-dung and four flies were reared from this substance. There is 

 no evidence, however, that in a state of nature the flies will lay their 

 eggs in anything but cow-dung. 



The time and manner of oviposition were puzzling at first. After 

 hours of close watching of fresh dung in pastures close to grazing cattle 

 not a single Hreinatobia was seen to visit the dung, much less to lay an 

 egg. This close observation was made at all times of the day from 

 dawn till dusk without result, while breediug-cage experiments were all 

 the time proving that nearly all fresh droppings contained many eggs. 

 With some hesitation, therefore, the inference was made that the eggs 

 were presumably laid at night, as stated in the note upon p. 60 of the 

 August number of Insect Life. 



The question was, however, considered by no means settled, and on 

 the discovery of the fly at Rosslyn Mr. Marlatt was directed to make 

 especial observations upon this point. The first result was that careful 

 examination of dung dropped in the early morning (prior to 7 a. m.) 

 showed very few eggs, not more than eight or ten to a single dropping, 

 while that dropped between 4 p. m. and later in the night contained still 

 fewer. On a dung dropped between 10 and 11.30 a. m. in the hot sun- 

 shine, however, examination, a few minutes after, showed a large num- 

 ber of eggs — estimated at three hundred and fifty. Other very fresh 

 droppings were examined and the eggs were found to range from none 

 at all to over three hundred. One animal was then fortunately ob- 

 served, from close quarters, in the act of passing her dung. As the 

 operation commenced, forty or fifty of the flies moved from the flank to 

 the back of the thigh near the "milk mirror," and at the close of the 

 operation they were seen to dart instantly to the dung and to move 

 quickly over its surface, stopping but an instant to deposit an egg. 

 The abdomen and ovipositor were fully extended and the wings were 

 held in a resting position. Most of them had left the dung at the expi- 

 ration of thirty seconds, while a few still remained at the expiration of 

 a minute. Every individual had returned to the cow, however, in little 

 more than a minute. This explains the previous non-success in observ- 

 ing tbe act of oviposition, for the Virginia cattle on the large stock- 

 farms are comparatively wild, and although the dung was examined as 

 speedily as possible after dropping, the flies had already left. 



The results, therefore, indicate that the eggs are deposited during 

 daylight, chiefly during the warmer time of the day, between 9 and 4, 

 and mainly between 9 in the morning and noon. They are laid singly, 

 and never in clusters, and usually on their sides on the surface of the 

 wet dung; seldom inserted in cracks. 



