CALIFORNIA FISH AND GAME 279 



then I have found a mule deer with a tape worm (Moniezia), but both 

 these and round worms have not been found in more than 2 or 3 per 

 cent of the dead deer I have examined. 



EXTERNAL PARASITES 



External parasites such as hot flies, wood ticks, and deer flies, are 

 the indirect causes of serious loss among mule deer. The deer bot fly 

 (Cephenomia pratti) is widespread and causes much suffering and loss 

 among our mule deer. On June 20, 1927, in Yosemite, I watched an 

 adult doe attempting to escape the attack of a bot fly. In domestic 

 sheep and in reindeer bot flies have been observed to deposit their eggs 

 directly into the nostrils of their victims. Although I have watched 

 bot flies in deer for many hours I have never been able, although close 

 enough (15 to 20 feet) to follow clearly with binoculars all the move- 

 ments of the bot fly, to detect the depositing of eggs directly into the 

 nostril of the deer. Whenever the doe observed in Yosemite found that 



Fig. 108. Larva of deer bot fly (x2) which infests the internal 

 nares and turbinal passages of the deer's nose, causing much pain 

 and loss among both mule and black-tailed deer, August 3, 1928. 

 Mus. Vert. Zool. No. 5793. 



the bot fly came within six inches of her nose she would shake her head 

 violently and stamp her front feet. At other times she would raise 

 her hind leg and extend it forward so that her nose was protected on the 

 inside by her body and on the outside by her hind leg (see Fig. 107), 

 At such times she was observed to lick her hind leg, possibly using 

 her tongue also to protect her nostrils from the bot fly. 



Some of the bot flies are successful in depositing eggs, for in the 

 majority of fresh mule deer heads that I have examined in California 

 I have found from 1 to 34 larvae of the deer bot fly in the frontal 

 sinus or throat of the deer. I have been unable to detect any difference 

 between the bot flies which infest Columbian black-tailed and California 

 mule deer. Apparently the same bot fly attacks both species of deer 

 in Yosemite. The larvae of the bot fly have a row of dark, stiff, 

 bristle-like organs along the top and on both sides of their bodies (see 

 Fig. 108) which protrude and prevent the living larvae from being 



