A spider (usually limited to individuals of a small species), or spiderling after hatching, will climb as high as it can, stand on raised legs with its abdomen pointed upwards (“tiptoeing”), and then release several silk threads from its spinnerets into the air. These automatically form a triangular shaped parachute which carries the spider away on updrafts of winds where even the slightest of breezes will disperse the arachnid. The Earth’sstatic electric field may also provide lift in windless conditions.
Many spiders use especially fine silk, called “gossamer“ to lift themselves off a surface, and silk also may be used by a windblown spider to anchor itself to stop its journey. The term “gossamer” is used metaphorically for any exceedingly fine thread or fabric. Biologists also apply the term “balloon silk” to the threads that mechanically lift and drag systems.[further explanation needed]
It is generally thought that most spiders heavier than 1 mg are unlikely to use ballooning. Because many individuals die during ballooning, it is less likely that adults will balloon compared to spiderlings. However, adult females of several social Stegodyphus species (S. dumicola and S. mimosarum) weighing more than 100 mg and with a body size of up to 14 millimetres (0.55 in) have been observed ballooning using rising thermals on hot days without wind. These spiders use tens to hundreds of silk strands, which form a triangular sheet with a length and width of about 1 metre (39 in)
(From Wikipedia, March 2015)