Spiders undergo and average of 5 and 10 moults in their lifetime, with the larger species tending to moult more, and can moult up to 20 times. Spiders moult their skins as many as 8 times before reaching adulthood.
The new cuticle is very soft and this means the legs are unable to support the body weight, so small spiders suspend themselves from a silk thread, and large species make a silk mat to lie on and moult on their backs to allow the legs to harden.
During the moulting process they can lose a leg, which will be regrown at the next moult. When the spider's cuticle is stretched to the limit the spider can grow only by moulting. Spiderlings may moult every few days, and increase in size with each moult. The time between moults increases with age. When a spider is about to moult it will stop eating, stay immobile, and some species seal themselves inside a silk-lined chamber while the old, outer layer separates from the new layer. The new cuticle is soft and pale.
The old cuticle or exuvium is often mistaken for a dead spider. The cuticle hardens and takes on normal colouration within a few hours.
The main purpose of spider venom is the speedy immobilization of prey. This enables the spider to prey on animals larger that itself, and animas that have dangerous defences, e. g. stings. Once the prey is immobile the spider can kill and eat it or keep it alive, but wrapped safely in silk.
So spiders that prey on large insects tend to have faster acting venom than those that prey on small or safe insects. Also a spider can control the amount of venom it injects as it bites. As far as humans are concerned, there are only about 200 species of spider with venom harmful to man; perhaps the most notorious is the Black widow and its relatives.
A few species of spider live in groups, and are considered social, e. g. Anelosimius eximius spins webs that can contain over 100,000 individuals.
Spider life cycle
Eggs. Spider eggs are round and approximately 1 mm in diameter. They are laid in a batch and covered with silk. The eggs vary in colour, and the number laid depends mainly on the size of the female and her health. For U. K. species this can range from 2 - 2000. Some species produce just one sac of eggs, whilst others may produce more, but the sacs will contain fewer eggs. Oonops domesticus lays just 2 eggs in each sac, and she will make fewer than 6 sacs in her lifetime.
Spiderlings. The eggs hatch about a week after they are laid, but the spiderlings stay in the sac. In most species, on hatching from the egg the spiderling has no hair, colouring, claws and it cannot feed itself, basically it is just an egg with legs. During this stage they continue to get nourishment from the yolk of the egg.
A few days later, after it has absorbed all of the remaining yolk, it moults. Only after this moult does it have hair, claws, the ability to see, eat and spin silk. Normally all of this takes place inside the egg sac, and it will remain in the sac for a few more days, or even months depending on the season. There may be some cannibalism during this time. The method of growth from this stage varies with species.
- Some may be carried around and fed by their mother
- Some may feed on their mother
- Others may have to make their own way in the world as their mother will already be dead
The spiderlings are just small versions of the adult, and will continue to moult, growing larger with each moult. Only when they have reached sexual maturity will the epigyne - in females - appear.
A startled spider will fall to the ground with its legs curled around its body. It can be picked up and rolled around in the palm of your hand, and still pretend to be dead, It will not do this when attacked by another spider however.