THE LIFE OF THE SPIDER 29 



tilts its abdomen upward (Plate V). The threads from the spin- 

 nerets are seized and drawn out by the air currents. Although the 

 dragline threads are often used, those from several spinnerets may 

 stream out in long filaments. When the pull on the threads is suffi- 

 ciently strong to support the weight of the aeronaut, it lets go of 

 the substratum and is pulled into the air. Spider lings balloon in 

 different ways, and some of them when afloat climb on their threads 

 like little acrobats, pulling in and winding up or streaming out more 

 filaments, and in this way exercising some control of the ship they 

 are flying. 



Not the exclusive habit of a single species, as was once supposed, 

 or limited to part of any season, ballooning goes on during much of 

 the year and is easy to observe. In the spring and during the fall 

 months, when immense quantities hatch from the egg, emerge from 

 their egg sacs and fly, the ballooning spiders by their very numbers 

 force themselves upon our attention. Small spiders can be inspired 

 to take off if one blows steadily against them; they tilt up their 

 abdomens, assume a ludicrous pose, and then bound into the air. 

 Because they are so tiny and weigh an insignificant amount, spider- 

 lings are sometimes at the mercy of the air currents and are lifted 

 into the air when they least expect it. Even larger spiders, caught 

 while dropping on their threads, are blown some distance. The 

 small aeronauts seem to float on streamers only a yard or two in 

 length, but the lines may actually be several times as long. In the 

 days of Aristotle, it was commonly believed that the spider could 

 shoot out its silk as the porcupine does its quills. We know now 

 that the spider must depend on breezes to pull the threads from its 

 spinnerets and to bear it aloft after the volume of silk is great 

 enough to support its weight on the air currents. 



How far do spiders fly on their silken filaments? Darwin recorded 

 the arrival on the Beagle of "vast numbers of a small spider, about 

 one tenth inch in length, and of a dusky red color," when the ship 

 was sixty miles from the coast of South America. He watched them 

 and observed that the slightest breeze was sufficient to prompt them 

 to sail rapidly away, after letting out new lines to catch the wind. 

 Even greater distances have been covered by these tiny aeronauts, 

 which have been known to alight upon the rigging of ships more 

 than two hundred miles from the nearest land. Because they move 

 upward and forward at a substantial pace, and because of their tiny 

 size, the spiderlings are quickly lost to sight. The average distance 

 they span can only be conjectured. The spider may be dropped to 



