64 



MISC. PUBLICATION 631, U. S. DEPT. OF AGRICULTURE 



Biology and Pathogenesis. — The parasitic habit is obligatory to 

 this species; it cannot exist in carrion. Eggs are deposited in oval 

 masses of 10 to 393 each, usually glued tightly to dry tissue near the 

 surface of a wound. They hatch in 11 to 21 hours. The larvae pene- 

 trate the tissue in a characteristic head-downward position, with the 

 posterior spiracles exposed to the outer air: they are gregarious and 

 produce characteristic pocketlike injuries. After feeding from 4 to 

 8 days, they drop to the ground and enter the soil to pupate. The 

 pupal stage varies from 7 days in summer to 54 days in winter under 

 Texas conditions. The average life cycle in summer at Dallas, Tex., 

 is about 24 days. Adults are known to live 65 days in captivity, al- 

 though they probably do not usually live so long, in nature. They 

 are known to feed on manure, meat, and exudations from wounds. 



<?*■ 



Figure 26. — Lateral view of mature third-stage larva : A, Callitroga americana ; 

 B, C. macellaria. Anterior spiracles and some spines are shown more en- 

 larged. (After Laake, Cushing, and Parish (77).) 



This is the most serious myiasis-producing calliphorid in the New 

 World. It is strictly parasitic and attacks only fresh, clean wounds 

 in man or animals. It is a serious plague of livestock, particularly of 

 cattle, sheep, and goats, over a part of its range. When not controlled, 

 an infestation of 20 percent or more of the livestock population may 

 be attained, with mortality in certain classes reaching 20 percent or 

 more of those infested. 



In infested areas man is often attacked. In 1935, when a severe 

 outbreak in the South caused more than 1,200,000 cases in livestock 

 in Texas alone, there were 55 recorded human cases and probably 

 twice as many unrecorded ones according to Dove (•!£)• Numerous 

 other cases have been reported from various parts of North, Central, 

 and South America. 



Any wound however small — even a scratch or a stubbed toenail — 

 may become infested. Larvae have been shown to be capable of enter- 

 ing the unbroken skin of guinea pigs and rabbits, and such an entrance 



