ARTHROPOD A 79 



known house centipede, Scutigera forceps. Fig. 57, is supposed by many 

 to be very poisonous and, according to Marlatt, it has a decidedly 

 disagreeable bite, which may be alleviated by the prompt application 

 of ammonia; it feeds on roaches, flies and other insects, probably in- 

 cluding bedbugs, so that it is a useful animal except for its poisonous 

 bite. 



PiG. 57. House centipede, Scutigera forceps. X/3- (From Marlatt, The House 



Centipede.) 



The millipedes, Julus and others, Fig. 58, are harmless to man 

 but are often destructive to crops. 



Arachnida. The economic importance of this group, which includes 

 some animals of great zoological interest, is not great and is very largely 

 negative. 



Spiders, Figs. 59 and 60. Some of the web-building spiders have a 

 slight positive importance from the fact that the fine threads that they 



FIG. 58. A milliped, Julus. X%. 



spin may be wound upon a reel and used for the cross-hairs of surveying 

 and other instruments of precision. They are also of some value as 

 destroyers of insects. Popularly the spiders are, as a group, supposed 

 to be poisonous, even dangerously so. Students of spiders, however, 

 have generally maintained that, with the exception of the huge, hairy 

 tarantulas of warm climates, the North American spiders are harmless. 

 Recently Kellogg (102) has pointed out that the notorious black widow 



