CLASS ARACHNIDA 



307 



the chelipeds of the decapod Crustacea. There are four pairs of hing 

 books opening by spiracles on the under surface of the abdominal meta- 

 meres from the third to the sixth. 



Scorpions live mostly in tropical and subtropical regions and are 

 nocturnal in their habits. Their food consists of spiders and large 



B 



Fig. 210. — Mites. A, an itch mite, Sarcoptes scabiei DeGeer. Male from above. 

 Greatly enlarged. B, Texas cattle iever tic]i., Margaropus annulatits (Say). Male. X 16. 

 C, chigger, Trombicula irritans (Riley). Larva. X 75. D, adult of chigger. Greatly 

 magnified. {A, C, and D from Ewing. ''Manual of External Parasites," by permission of 

 the publisher: Charles C. Thomas; C after Oudemans: B from, Salmon and Stiles, " Cattle Ticks 

 of the United States," Bur. An. Indus., U. S. Dept. Agr.) 



insects which they seize with the pincers of their palpi and sting to death. 

 The sting also serves as a weapon of defense. It is, however, impossible 

 for the scorpion to sting itself to death, as it has often been said to do. 

 The sting rarely, if ever, proves fatal to man. 



331. Mites. — Another group of arachnids contains the mites (Fig. 

 210), which in turn include the ticks. These are very small arachnids 



