Growth and Development

SPIDERS - Growth and Development

                Spider eggs have large yolks compared with those of insects and, in any batch of eggs, there are often infertile eggs left by the mother to provide the spiderlings' first meal. Because their exoskeleton does not stretch, spiders shed their skin as they grow; the first of these moults often take place within the egg sac.

The females of some huntsmen and crab spiders must cut a hole in the egg sac in order for the spiderlings to emerge, otherwise they starve to death. In a number of spider groups, the female cares for the young before they disperse. She may catch prey and share it with them or, in the case of some comb-footed spiders, actively feed them from her mouth. In many species, the female dies before the spiderlings hatch and she becomes their first meal.

Wolf spiders are perhaps the most devoted mothers - the female carries her egg sac everywhere, attached to the end of her abdomen. When the eggs hatch, the spiderlings climb onto her back and hold on to specially designed knob-shaped hairs on her abdomen until they are old enough to disperse.

After hatching, spiderlings of most species play out a long line of silk on which they "balloon" away to disperse on the slightest breeze. This is remarkable effective, as spiderlings have been found more than 4 km above the Earth! Once they land, the young spiders begin to feed almost immediately and web-spinning species set up their first web, usually slightly different in form to webs spun later in life.

Predators are a constants threat from the moment the eggs are laid and small parasitic wasps and flies which lay their own eggs on the spiders account for a large mortality rate. Moulting is a particularly dangerous time, when the spider's body is soft and immobile for an extended period and is vulnerable to even the smallest predators. As a consequence of these trials, usually less than one percent of spiders survive to maturity and these are indeed lucky spiders.