Although many spider eggs hatch in the spring, there are some that hatch in the fall. Most spiderlings stay within the egg sac until they undergo their first molt – their small cast skins can be seen inside the old egg sac. After molting they emerge and cluster together, still living largely upon the remnants of yolk sac in their abdomens. In several days the spiderlings are ready to disperse, which is necessary to avoid competition for food and prevent cannibalism among the hungry siblings.
Some species, especially ground dwellers, disperse by walking, often over relatively short distances. Others, particularly foliage dwellers and many web builders, mainly disperse by ballooning. To balloon, spiderlings crawl to the top of a blade of grass, a twig or a branch, point their abdomens up in the air and release a strand of silk. Air currents catch the silk, often called gossamer, and lift the spider up and carry it off. Aerial dispersal may take a spiderling just a few feet away or much, much farther – spiderlings have been found as far as 990 miles from land. (Charles Darwin noted spiderlings landing on the rigging of the Beagle, 62 miles out to sea).