GASTEOPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 15 



to place without eating, their lips resting upon one another, or they 

 may congregate with cattle, which are not subject to attack. The 

 horses spend such days in awaiting darkness, after which feeding 

 takes place. Characteristic positions of the animals are shown in 

 Plate III. 



Wind with a velocity of 15 miles an hour or more greatly relieves 

 the animals, and persons driving horses about thrashing machines 

 often stop them so that they face the breeze. 



Cloudiness is also a protection to horses, and if only a light cloud 

 conceals the sun a bunch of horses may be observed to disperse and 

 begin grazing. Often their feeding will have only begun when the 

 sunlight returns, causing them again to seek protection in a group. 



Horses in standing water are not annoyed by nose flies and fre- 

 quently they seek this protection in order to eat, despite the fact 

 that hundreds of mosquitoes feed upon each animal. This standing 

 or feeding upon grass in water is excellent for a foundered horse, 

 and the mud which adheres to his legs prevents G. intestinalis from 

 ovipositing upon them. 



While the wind and cloudiness are especially protective against 

 G. haemorrhoidalis, the other two species of bot-flies are not much 

 affected thereby. G. intestinalis may be observed to oviposit on 

 windy and cloudy days. G. nasalis deposits under more adverse 

 conditions than does G. haemorrhoidalis, but seems to be more sensi- 

 tive to natural agencies than is G. intestinalis. 



In barns the species of Gastrophilus never have been observed to 

 oviposit. On numerous occasions ovipositing adults have been ob- 

 served to pursue the animal only until it reaches the stall door. 

 Post-mortem examinations of horses which had been confined in 

 stalls failed to reveal a single larva. One of our correspondents 

 reports that the annoyance of G. haemorrhoidalis was greatly re- 

 duced when he constructed a simple shed in the pasture where the 

 horses could congregate. 



SEASONAL HISTORY OF GASTROPHILUS. 



At Aberdeen, S. Dak., the larva? of G. haemorrhoidalis are ob- 

 served attached to the margin of the anus of horses as early as May 

 5 to 10, and if suitable temperatures occur adults may be expected a 

 little prior to June 15. 



From June 21 to 27, 1915, G. haemorrhoidalis adults appeared at 

 Lodge Grass, Hardin, Billings, Miles City, and Custer, Mont. At 

 the same time they appeared at Aberdeen, S. Dak., and neighboring 

 points. They have been observed at Aberdeen, S. Dak., as late as 

 October 10. though they are seldom found after a killing frost, which 

 is usually about September 15. 



