3 o AMERICAN SPIDERS 



the earth near the site of its departure, but it can fly again and 

 again, and thus accumulate a substantial dispersal distance. 



Most ballooning goes on at reasonable heights, probably less 

 than two hundred feet, as was noted by McCook; but sometimes 

 powerful air currents carry the creatures to great heights. During 

 an aerial survey in Louisiana, B. R. Goad found spiders and mites 

 well represented in samples of aerial fauna at 10,000 feet, and they 

 were even more frequent in the catches of from 20 feet up to 5000. 



Ballooning has made possible the distribution of spider species 

 over the world. Species have been enabled to send pioneers in num- 

 bers into new areas of all kinds. Oceanic islands have received their 

 spider population almost exclusively through this colonizing mech- 

 anism. On the bleak cliffs of Mt. Everest, at an elevation of 22,000 

 feet, Kingston found tiny jumping spiders hopping about on the 

 surface and hiding underneath stones. These could easily have been 

 carried upward by the air current. On the other hand there is a pos- 

 sibility that they were permanent residents living at an elevation 

 too high for almost any other creature, and undoubtedly existing on 

 small insects unnoticed by Hingston. 



In the temperate zone aeronautic spiders are most numerous 

 during Indian summer, when balmy days follow cool nights. In 

 1918, J. H. Emerton studied the aerial fauna in Massachusetts and 

 listed sixty-nine species that took to the air during the days of his 

 observation. A considerable number of these spiders were fully 

 mature, others were advanced in their age, but all were of rather 

 small species. It is now well known that many adult and half-grown 

 spiders fly, and that this curious activity is not confined to spider- 

 lings just emerging from their egg sacs. Emerton characterized the 

 males of Zygoballus terrestris, a stocky little jumping spider, as be- 

 ing "a regular autumn flyer." Males of some of the smaller orb 

 weavers, such as Aranea pegnia and A. displicata, may be seen 

 ballooning on sunny afternoons, floating a few feet above the 

 ground on long filaments. 



It is probable that almost all groups of true spiders use this 

 interesting dispersal device during at least some part of their life. 

 Those that shun the light during all their life may not resort to 

 flying; and only a few of the mygalomorph spiders are credited 

 with this activity. The tarantulas are not known to balloon at all, 

 and the large size of their young would seemingly preclude such 

 activity. The purse- web spiders, notably the European Atypus 

 piceus, disperse by taking to the air for short distances, so it is prob- 



