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Reproduction in Spiders

Aug 18, 2007
Like all animals spiders need to reproduce and there are two main elements to this reproductive process.
First there is that anatomy and physiology of the reproductive organs and secondly there is the ecology of boy meets girl.

The reproductive ecology of spiders basically involves three steps:
1) a male has to find a female
2) he has to succeed in mating with her
3) the female has to lay and protect the eggs.

Within this simple plan spiders have evolved a wonderful range of strategies and behavioural characteristics. The greatest diversity of characteristics is found in the moments immediately after contact. Spiders are carnivores, and cannibalism is quite acceptable to them.

In many species the male has to work hard to convince the female that he is a potential mate and not dinner because there are species where the female often eats the male before mating (and/or after mating) and there are also species where the male and female live together in the same web but the male is able, one way or another, to leave the female and depart from her web after mating. The idea that all female spiders always eat their mates just isn't true.

The male will follow the traditional courtship rituals and as you can imagine male spiders tend to approach the females cautiously until they they are convinced the female knows who they are and even then many of them like to have some insurance. In many species the males have worked out clever methods to ensure their survival, in others the male is so small he is of no interest to the female and in a lot of cases the two live together quite happily.

It has been documented that a lot of adult male spiders simply die of hunger and exhaustion because they spend all their energy finding and courting females and never stop to eat!

When a male spider reaches maturity and is ready to start looking for a mate he first spins a sperm web. This structure varies from family to family, but generally it consists of a few support strands and a small triangle of tight web at or near one edge. The male spider then places the epigastric furrow of his abdomen against the triangle and (often rocking up and down) releases a drop of sperm on to it. Then he dips his pedipalps into the sperm which absorbs some of the sperm, often he will moisten the tips of his pedipalps with his mouthparts first, and he may also climb under the web and then reach up and around to load his pedipalps.

The genus Scytodes offers one good example of a variation. Here the sperm web has been reduced to a single thread which the male draws across his genital opening with his 3rd pair of legs. The drop of sperm collects on this and is then transferred to the pedipalps.

Then the male spider sets out in search of a suitable mate. His searching involves checking out areas of suitable habit, and when he is close to a female spider the pheromones and chemotactic responses he gets will ensure the intended female is of the correct species.

Male wolf spiders are known to recognise and follow the draglines of females. Also males often mature early than females because they are smaller and go through one or more less moults. In some cases this allows the males time to find a female before she is mature. In such cases he will often move in next door. This not only ensures he will be there after she has gone through her final moult, but also gives her a chance to become accommodated to his presence to some extent.

Female spiders also show variation in the way they prepare and then look after the eggs and the egg sac after mating. Some spiders (such as Heliophanus Cupreus) simply lay their eggs in their own silk retreat, stretching a few strands of silk over them and then guarding them until they hatch.

Most species however spin much more substantial cocoons or egg-sacs to hold the eggs safe. This is particularly necessary to a species where the mother dies before the eggs hatch.

Other species both spin a protective cocoon and then keep it in their retreat and watch over it until the young hatch. The Orb-web spider (Araneus Quadratus) is an example of a spider that dies as winter closes in but whose eggs survive the winter to hatch in the following spring or early summer.

Wolf spiders in the genus Pardosa however, and Nurseryweb spiders in the genus Pisaura both live to see their young hatch. Both of them spin a protective cocoon for the eggs and both of them carry the cocoon around with them. They differ however on how they carry it, Pardosa carries hers attached to her spinnerets while Pisaura carries hers with her chelicera.

When an Orb-web spider spins a cocoon she first spins a circular base plate for the newly hatched spiders to live in until their first moult. Then from below she spins a cylinder to make the sides, then lays her eggs and then spins another plate called the cover plate. The whole thing is then wrapped in one or more layers of protective silk and suspended somewhere.

In comparison Wolf spiders spin a similar construction but they add the cylinder walls from above. Some spiders hang their cocoon from threads after it is made, others build the cocoon with the base solidly attached to something. In this way the clubionid (Agroeca Brunnea) spins a flat cocoon that resembles an upside down wine glass. The female adds bits of soil to the outside of the cocoon to help it blend in to the background giving it a very sophisticated camouflage.

As far as looking after the brood goes, the female may tear open the the cocoon so that the young spiders (spiderlings) can escape, she may carry them on her back until after their first moult and in a number of cases she will feed them with the prey she herself has caught. The cocoon offers protection from cold, from desiccation and to some extent from predators and parasites. The downside is that some birds collect them to line their nests.

Different species of spiders produce different amounts of eggs per cocoon. Also some spiders produce two or more cocoons in a year, and some such as tarantulas may live for many years producing young every year. It is not possible therefore to state clearly what the reproductive effort of spiders in general is.

Consider also that the health and size of any individual female spider varies and this also affects the number of eggs she can produce. As a general rule larger spiders produce more eggs but there are always exceptions.
About the Author
Nikki Fox has been afraid of spiders all her life.
Now she has hit back at them and has created a website to share her discoveries.
Visit www.spiderpanic.com for her tips and advice on arachnophobia and spider prevention.
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