238 AMERICAN SPIDERS 



in the use of spiders for biological control have been made to in- 

 dicate their possibilities in this field. 



Economic entomologists have acknowledged the importance of 

 specific spiders as control agents in certain cases. For example, in 

 the Fiji Islands the cocoanut palm is ravaged by a moth that fre- 

 quently occurs in tremendous numbers. During each outbreak, one 

 of the large, strikingly ornamented jumping spiders, Ascyltus ptery- 

 godes, increases rapidly in numbers and attacks the caterpillars and 

 pupae that survive the efforts of other controls. Again, various 

 workers in America have identified spiders as important factors in 

 checking cotton worms, gipsy moths, pea aphids, and many other 

 destructive insects. They are especially effective in a prepared 

 environment such as a cotton or corn field. In any cultivated locale 

 many kinds of insects will take up their abode, but the varieties that 

 are detrimental to the plant crop are present in concentrated num- 

 bers. Spiders quickly overrun such areas and account for a con- 

 siderable percentage of the larvae and adults of the pest. Both the 

 vagrant species and the web spinners are important here. Their 

 catch, when examined, is found to consist largely of the noxious 

 insects. 



If spiders are evaluated on the basis of their direct effect upon 

 man in terms of nuisance, disservice, and usefulness, the conclusion 

 is that they are essentially neutral. They litter our houses, but their 

 unsightly, dust-catching cobwebs render us a distinct service in 

 disposing of mosquitoes and flies that have got through our window 

 screens. We find a use for their threads in certain types of optical 

 instruments; the Papuan natives use their matted webs for silken 

 lures and fishnets. Although attempts have been made to rear spi- 

 ders and take their silk for fabrics, the results have been unsuccess- 

 ful. To the diet of the Laos of northern Siam their bodies add 

 much needed fats and proteins, otherwise not obtainable. Spiders 

 feed on a great many beneficial insects as well as on undesirable 

 ones. On the other hand, their bodies provide food for game fish 

 and for birds. And finally, the bites of a few spiders are poisonous 

 to warm-blooded animals. Thus one effect cancels out another. 



MEDICAL IMPORTANCE: THE SPIDER'S BITE 



Inasmuch as spiders are predators that normally specialize on 

 insects and only rarely come in contact with human beings, their 



