132 



GENERAL ZOOLOGY 



year itch, is caused by a mite, Sarcoptes scabei, which lives 

 in little tunnels in the skin. Another mite, Demodex 

 folliculorum, commonly lives in the oil glands of the skin, 

 particularly those on the nose and face, but apparently 

 does no harm. The scab-parasite, Psoroptes communis, 

 attacks sheep, cattle, and horses, causing sores on the 

 skin. 



FIG. 61. Mites and ticks. A, B, nymph and adult of chigger, or harvest mite; 

 C, the follicle mite, Demodex; D-G, ticks: male, female, larva and nymph. 



Ticks are larger than mites and adult females become 

 greatly swollen, some reaching the size of a lima bean. 

 The cattle tick, Margaropus annulatus, is the best known 

 representative in this country. An adult female of this 

 species, after filling herself with blood, drops to the ground, 

 and lays several thousands of eggs. As soon as the six- 

 legged "seed ticks" hatch, they climb up to the top of the 

 nearest grass and await the passing of some animal which 



