ARACH NIPS, CENTIPEDES, AND MILLIPEDES— ARTHROPODS 201 



web would not bear as great a weight as the spider web. Spider web is 

 impervious to variations in temperature and humidity and, therefore, is 

 not altered in its position by extremes in climate. The collection of this 

 web for commercial use is quite simple. A spider, frequently the black 

 widow, is held on the end of a stick and pushed off with another stick. 

 As it is pushed off it fastens a web to the first stick and lowers itself 

 gently to the floor, spinning web as it goes down. This single strand is 

 clipped loose and the spider is picked up on the stick and the process 

 repeated over and over again. 



The bad reputation which the spiders have among the general public 

 can be traced to the fact that they have fangs and poison, and some of 

 them can give a rather painful bite. They are not particularly vicious, 

 however, and bite only in self-defense. There is only one in the United 

 States that can cause serious symptoms in man, the black widow. This 

 is not a large spider, but has poison sacs that extend far down into the 

 body and thus can inject a rather large amount of poison. This, coupled 

 with the fact that the poison is of high potency, accounts for its serious 

 effects on the human body. Bites are comparatively rare, considering 

 the wide distribution and abundance of this spider, because the black 

 widow is rather shy and retiring. However, a female protecting an egg 

 case will bite rather readily when disturbed, and most bites are received 

 in this way. The poison is of a neurotoxic type, nerve poison, and 

 causes severe systemic reaction for several days after the bite. Some of 

 the symptoms are pain in the muscles, difficulty in breathing, nausea, 

 mental confusion, and general retardation of the body functions. While 

 the symptoms are very serious and not to be minimized, the bite is fatal 

 in only rare instances and then only in unusual circumstances. 



Reproduction among the spiders is very interesting, and a study of 

 this process among the black widows may serve as a typical method for 

 the group. Spiders are ordinarily solitary animals ; that is, they do not 

 live in social groups. There is a good reason for this lack of sociability ; 

 spiders are cannibalistic and often prey on one another when they are 

 confined to close quarters. During reproduction, however, there must 

 be some association and the cannibalistic tendencies are repressed tem- 

 porarily at this time. A female ready for reproduction will get in the 

 center of her web and wait for a male. Some studies show that she 

 casts out single strands of web which are carried a considerable distance 

 by the wind. When a male contacts one of these strands he picks up 

 some sort of telegraphic signal which indicates that the female is ready 

 for insemination. He can follow the strand of web and it will lead 

 him to her. The male is much smaller than the female and he ap- 

 proaches her with great caution. He will come in slowly and then turn 



