238 Zoology of Colorado 



which lives on vegetation, and occasionally enters houses in vast 

 numbers, causing alarm. Species of Tetranychus (so-called red 

 spider) occur on the leaves of orchard trees and on greenhouse 

 plants, spinning a fine web over the leaf surfaces. They are quite 

 injurious to vegetation. Ewing described a new species, T. 

 weldoni, found in Colorado on apple, prune and cottonwood trees. 

 The scab of sheep is caused by a mite (Psoroptes) and there are 

 various other mites infesting domestic animals, fowls, and even 

 man. Recently it has been shown that a serious disease of 

 honey bees is due to a mite living in the breathing tubes, but this 

 has fortunately not reached Colorado. 



SPIDERS (ARANEIDA) 



The true spiders have a cephalothorax, that is head and thorax 

 all in one piece. The abdomen in all our species shows no segmen- 

 tation, the eyes are numerous, and the legs number eight. The 

 Colorado spiders are much too numerous to describe or even 

 enumerate, but a few conspicuous types may be mentioned. The 

 large fat-bodied species which spin circular webs about buildings 

 belong to the genus Epeira. It is richly represented in Colorado 

 with fifteen species. Related to it, but more or less silvery, with 

 the more elongate abdomen transversely barred, are our two 

 species of Argiope, both of which have been found on the Uni- 

 versity of Colorado campus. The Crab-spiders, squatting down, 

 with the legs at the side after the fashion of a crab, constitute the 

 family Thomisidae. The most interesting one is Misumcna 

 vatia, which sits on flowers, catching the bees and other visitors 

 as they come. It varies from white to deep yellow, and usually 

 matches the flower in color; but on pink flowers yellow spiders sit 

 and appear to do good business. Can it be that some of the 

 insects do not distinguish between pink and yellow? The jump- 

 ing spiders, or Attidae, are very characteristic. They do not spin 

 webs, but actively hunt their prey. We have many species, the 

 most common belonging to the genus Phidippus, one member of 

 which is bright red above, and extraordinarily resembles a wing- 

 less wasp of the family Mutillidae. The wasp stings viciously; 

 can it be that the spider is protected from its enemies by the 

 resemblance? The Lycosidae, or Wolf-spiders, are some of them 



