DIPTEROUS LARV.E 63 



of which tmie, having reached its larval maturity, it detaches from the 

 mucous membrane and passes to the nasal passages from which it is 

 expelled by the violent sneezing which it excites in its host. Having 

 reached the ground, it quickly buries itself, contracts withm its smooth 

 dark shell, and enters upon its pupal stage (Fig. 33, 3). After from four 

 to six weeks of pupation the mature insect emerges. 



Effect. — Both sheep and goats suffer from the attacks of this fly. 

 Sheep are especially disturbed by it, and in their efforts to avoid its 

 attack will toss the head, thrust the nose into the ground, or dash about 

 in frenzy. The grubs cause much 

 irritation to the sensitive mem- 

 brane which lines the cavities of 

 the head both by the booklets 

 with which they make their at- 

 tachment and by the spines cov- 

 ering the ventral region. Further- 

 more, if numerous, and the mucus 

 secreted is not sufficient for their 

 nourishment, the grubs will feed 

 upon the membrane itself. The 

 disturbance to the host will be 

 manifest accordmg to the number 

 of grubs present; if there are but 

 few, there may be no more than 

 a slight catarrhal discharge with 

 occasional sneezuig. In heavy 

 infestation there is a profuse 

 muco-purulent nasal discharge with frequent sneezing and tossing of the 

 head, the respiratory passages in some cases becoming so filled as to 

 bring the animal to the verge of suffocation. The appetite is lost, and 

 emaciation and weakness may progress until there is inability to rise, 

 death in such cases soon following. 



Tabular Review of Life History of (Estrus Ovis 



1. Adult Fly. — (June to October.) 



I 



2. Hatched Embryos. — Deposited in nostrils of sheep. 



\ 



3. Larvse. — Attached to lining membrane of sinuses of 



I sheep's head. Stages 2 and 3 approximately 



I 103^ months. 



4. Pupse. — Free; approximately 6 weeks. 



Fig. 33. — CEstrus ovis: 1 and 2, adult fly; 

 3, pupa; 4, full-grown larva, dorsal view; 

 5, same, ventral view; 6, young larva. 1 and 

 2 natural size, the others enlarged (after 

 Osborn, from Riley, Bui. No. 5, Bureau of 

 Entomology, U. S. Dept. of Agr.). 



5. Adult Fly 



