ECONOMIC AND MEDICAL IMPORTANCE 237 



of the nearly total lack of pertinent data on their feeding habits. 

 By comparison with ants, certainly in the tropics, spiders are less 

 important predators; but they are far more important than the 

 highly considered birds in the number of invertebrates that they 

 destroy annually. Spiders are ordinarily credited with catholic 

 tastes and charged with attacking and eating all kinds of insects 

 indiscriminately. This is a generalization that is subject to many 

 exceptions. Because such space web spinners as the orb weavers 

 and various sheet web weavers concentrate on flying insects, it is 

 probable that a higher percentage of their catch is made up of 

 beneficial insects. On the other hand, some of the hunting spiders 

 have been known to concentrate on obnoxious varieties. Much de- 

 pends on the location of the webs and the presence of wandering 

 vagrants at a site where flights or emergences occur. Webs heavy 

 with biting flies or annoying midges bear witness to the efficiency 

 of spiders in helping to control economically destructive insects. 

 One female black widow is reported to have destroyed 250 house- 

 flies, 33 fruit flies, 2 crickets, and one spider during its lifetime. 

 But in other locations similar webs may be filled with parasitic flies 

 and other types that are considered beneficial. 



Although spiders are not usually thought of as being efficient 

 agents of biological control, they have acted that role in a few in- 

 stances. During 1923 and 1924 there was a tremendous increase in 

 the numbers of bedbugs in Athens, particularly in the Greek ref- 

 ugee camps. Even when the inmates of the wooden barracks moved 

 out into the roads they could not get rid of the insects, which fol- 

 lowed their hosts with their usual persistence. Suddenly there came 

 a rapid decrease and by 1925 the bedbugs had been eradicated. 

 N. T. Lorando credited this phenomenon largely to the presence of 

 the predaceous crab spider, Thanatus flavidus. He was much im- 

 pressed by the efficiency with which it dispatched the bugs, de- 

 stroying thirty or forty a day, and with its possible exploitation for 

 systematic biological control. Later this spider was introduced 

 into animal laboratory rooms in Germany by A. Hase, and again 

 achieved great success in controlling bedbugs. Another member 

 of the same genus, Thanatus peninsulanus, is often found in great 

 numbers in warehouses in New York City, where it preys upon 

 the many pests of stored cereals and other products. This spider, 

 whose natural habitat is the Southwest, has probably been intro- 

 duced into several localities on the East Coast along with produce 

 from the holds of ships. In the main, however, too few experiments 



