Meteorological Aspects of Spider Ballooning

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Abstract
The importance of long-distance dispersal is recognized in the recolonization of disturbed habitats, but little is known about how migrant spiders respond to the various features of their atmospheric environment. Many spiders balloon by silken threads on wind currents for long distances and thus disperse to new habitats. Previous authors have focused on the meteorological conditions responsible for the initiation of spider ballooning. However, the meteorological conditions necessary for spiders to remain aloft on wind currents are less well known. During the fall and spring in east Tennessee, airborne spiders were collected from sticky traps extended from a 45-m tower at five heights throughout the forest canopy. Climatological data were collected continuously from the tower throughout the study. The results indicate that the most important meteorological factors affecting ballooning are abrupt changes in daily air temperature, maximum difference between dew point and air temperatures, and low wind fluctuations. For the fall, the highest percentage of spiders collected was at 22 m, immediately above the forest canopy, and for the spring, the highest catches were at 33 and 44 m. These results are correlated with sizes and taxa of animals trapped (i.e., more spider taxa with small body size ballooned in the spring than in the fall).