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CIVIC BIOLOGY 



The larger arachnids, in spite of their bad reputation and 

 terrifying appearance, are comparatively harmless. Even those 

 of the poisonous varieties, tarantulas and scorpions, make no 



attack upon man un- 

 less frightened or mo- 

 lested. Their economic 

 importance is not con- 

 sidered great, though 

 since they are insectiv- 

 orous, they may be dis- 

 tinctly beneficial. 



The smaller arach- 

 nids, mites and ticks, 

 cause great destruction 

 of vegetable and animal 

 life. They are charac- 

 terized by an unseg- 

 mented body, the abdo- 

 men as well as the head 

 being joined to the tho- 

 rax. While we must 

 not overlook the service 

 of some species as scav- 

 engers, we are con- 

 cerned much more with 

 them as parasites upon 

 living animals and 

 plants. 



Red spider Tetra- 

 nychida, " four-clawed." 



This greenhouse pest is found both indoors and out, and on 

 various plants and trees. It is one of the commonest families, 

 containing sixty species. The red spiders are most trouble- 

 some in times of drought and are found chiefly on the underside 



FIG. 80. Harvestmen clearing the plant lice 

 from a grapevine 



Photograph by the author 



