BLACK WIDOW SPIDER D' AMOUR ET AL. 411 



negatively heliotropic, tending to move away from the light. The 

 geotropism of the young provides a means of dispersal. Once the 

 maiden flight has been effected and dispersal accomplished, the spiders 

 no longer exhibit the tropism. The following observations on the 

 dispersal of the spiderlings were made by us. 



A glass tube about 1 % inches in diameter and 3 feet long, enclosing 

 a piece of bamboo of the same length wound with raffia, was closed 

 with cloth at both ends after a newly made egg sac had been placed 

 inside on the bottom cloth. The whole contrivance was then set 

 upright in a retort stand. The bamboo inside the glass tube would 

 furnish the spiderlings something to climb on should they have the 

 instinct to do so after emergence from the sac. About 4 weeks after 

 the spinning of the sac, there were two little swarms of 50 or 60 

 spiderlings each at the base of the tube near the sac. During the day 

 they all climbed their artificial tree and swarmed at the top of the 

 tube. The next morning the apparatus was carried out into the 

 country, the top cover removed, and the length of the artificial tree 

 increased by a 3-foot stick. Immediately about 15 of the little spiders 

 detached themselves from the swarm and intently climbed to the very 

 tip of the new stick. The sun was shining and a little breeze blowing 

 from the south. Suddenly a tiny mite was snapping about in space 

 18 inches or 2 feet from the stick. It was a spiderling waving in the 

 breeze at the end of a gossamer drag-line which it had spun as it was 

 blown from its moorings. Then the spider was observed to be working 

 its way back along the line; not drawing in the line but leaving it out, 

 possibly doubling it. The adventurer reached his dock again, leaving 

 the silken thread flapping in the breeze. Suddenly the line broke at 

 its base, or was cut by the spiderling behind him, and he sailed away 

 into space too rapidly for the eye to follow the course very far. This 

 happened again and again, till of the original 15 adventurers only 2 or 

 3 remained. This explains the disappearance of the young spiders 

 from the maternal web so soon after emergence, and explains also their 

 being found later in life in curious places to which chance blew them 

 on their initial flight. 



When the young spider ends its voyage we must imagine that it 

 seeks the first hole or crack available as shelter. Here it spins a 

 web not unlike that of the mother, but on a small scale, catches its 

 prey in the same way, and if circumstances are propitious, sets up a 

 permanent establishment. 



ENEMIES 



In spite of the fact that the poison of the widow is deadly to all 

 small animals, she has a number of natural enemies. We have ob- 

 served the vireo feeding the spider to her nestlings, and pigeons and 

 chickens may eat it with impunity, the latter with apparent relish. 



