366 



ECONOMIC ENTOMOLOGY 



and blisters formed are very irritating, and the disease may spread 

 rapidly. 



Sheep Scab Mite (Psoroptes communis var. ovis Furst). — This mite 

 burrows under the skin of sheep forming large areas of crust called 

 scabs. From these areas, commonly confined to the neck, back and 

 rump, the wool falls away. The disease is contagious. Each female 

 lays 15-24 eggs which hatch in 2-3 days; the young mites mature in 

 15 days. (See Farmers' Bull. 713, U. S. Dept. Agr.) 



Family Ixodid^ (Ticks) 



Cattle Tick {Mar gar opus annulatus Say). — In the Southern States 

 this tick causes large losses as the agent responsible for the Texas 



Fig. 241. 



—Rocky mountain spotted fever tick (Dermacentor venustus) : i, unengorged 

 female; 2, unengorged male. {Year Book, U. S. Dept. Agric.) 



Cattle Fever. It is a dark 8-legged creature. The engorged female 

 drops from cattle to the ground and lays its eggs. The young ticks 

 (seed ticks) on hatching crawl up nearby herbage and drop on the 

 backs of cattle as they brush by. Attached to the skin they feed 

 until they become mature. 



Rocky Mountain Spotted Fever Tick {Dermacentor venustus Banks). 

 — This tick, with others, is able to transmit the so-called "Spotted 

 Fever" of man in the Rocky Mountain states. It is possible that the 

 ground squirrel of the region serves as a reservoir of the virus. The 



