i8 AMERICAN SPIDERS 



cies, which tend to be less active and frequently are quite sluggish. 

 Many of these are bizarre animals that have beautifull sculptured 

 bodies, often set with strangely shaped spines, and short legs, fre- 

 quently armed with spines and processes. Many of them occur in 

 caves in our southern states, where they have developed some un- 

 usual types. 



Mites. Mites far surpass the other arachnids in numbers and 

 economic importance. Most are minute reddish creatures with un- 

 segmented, ovoid bodies fused into a single piece. The tiniest mites 

 are wormlike and suck plant juices, thereby causing galls, spots, and 

 blemishes on the foliage of trees and plants. Other pygmies live in 

 the tracheal tubes of bees and in the hair follicles of mammals, in- 

 cluding man. Some of the most gaily colored species have taken 

 to living in water and swim with the aid of long hairs on their legs. 

 The free living forms abound in detritus, where they prey on tiny 

 animals or eat decaying animals or vegetable matter. About half 

 the mites are parasitic and live on the bodies of animals all or a part 

 of their lives. 



Mites hatch from eggs as six-legged "larvae," an unusual physi- 

 cal phase for which we still have no adequate explanation. After a 

 period of feeding, the larvae change into eight-legged nymphs, which 

 undergo one or more nymphal stages before becoming the sexually 

 mature adults. 



Most pestiferous of all are the larvae of the harvest mites, known 

 to Americans as redbugs and chiggers, which attach to the skin and 

 cause violent itching and irritation. Some redbugs transmit Rickett- 

 sial organisms, which cause tsutsugamushi disease, or scrub typhus, 

 which is frequently fatal to man. The nymphs and adults of the 

 redbugs are innocuous creatures content to live on vegetable matter. 



Largest of all the mites are the ticks, whose leathery bodies are 

 capable of becoming greatly distended with blood, to nearly an 

 inch long in some females. Following engorgement, which is ac- 

 complished by forcing the beaklike mouth parts deep into the skin 

 of the host, the mature females fall to the ground and lay several 

 thousands of eggs. From them hatch six-legged larvae, called "seed 

 ticks," which climb on the body of a new host when opportunity 

 arrives. Some ticks use the same host during all their feeding, but 

 others require two or even three different kinds of hosts in order 

 to complete their life cycle. Many ticks attack man and are a great 

 source of annoyance because of their irritating bite. Among tick- 



