Order Araneae

Spiders. Over 40 000 species have been described so far, and around 660 in the U. K .

Spider parts of the body

The prosoma and opisthosoma are joined by a pedicel (see right which shows the underside of a mature female). The chelicerae end in fangs which usually have poison glands, and their legs end in claws.

Spiders can have six or eight eyes and the arrangement of the eyes is used in identification; however, vision is poor in most species, and used mainly for detecting movement. The wolf and jumping spiders which hunt down their prey usually have better vision. Spider eyes are not compound like those of insects, but simple, and usually arranged in two rows.

Most spiders have what are called book lungs (see the drawing below). These are blood-filled slices of tissue separated by an air space. Most species have one pair of lungs.

Each mature female has a pair of sperm storage sacs or spermathecae. The spermathecae are shed with each moult, so the female spider must mate after each moult. The palps of the males are modified to transfer sperm into the female's epigyne (genital opening) see above and left, which is located on the dorsal side of the opisthosoma. The epigyne of the female and swollen palps of the male (see below) are only seen in mature adults. Females are usually larger than males.

Silk. Most spiders (except wolf and jumping) catch their prey in webs. And web construction can be used to identify to family or genus. The silk comes from the spinnerets - see the drawing below (the number varies according to species, but 3 pairs is the most common) which are located on the underside posterior of the opisthosoma. Spiders do not stick to their own webs because they either step on the non-sticky parts only, or secrete a special oil on their feet. The silk is a fluid which hardens in contact with the air. It emerges as many very thin strands which join up to form one very strong strand. Silk is also used by the females to build egg sacs where the young remain for a few weeks. The wolf spiders carry the egg sac around with them attached to the spinnerets. The silk from Araneus diadematus is around 0.003 mm thick - that is just 10% of the thickness of silkworm silk.

Legs. Spider legs are divided into 8 parts - see the drawing below left. There may be 2 or more claws, and these may have teeth like a comb. Hunting spiders have a pad of hairs which, along with a sticky secretion, enables the spider to get a good grip on most surfaces.

Spider courtship, mating and behaviour

by the males can be elaborate, but much of this is to make sure that the female can distinguish him from a juicy meal! Before mating the male spider deposits a drop of sperm on the surface, and then transfers this to his palps which pick it up by capillary action. the male's palps fit into the female's epigyne like a key fits into a lock. This prohibits mating with the wrong species. In

species which spin webs the male will pluck and vibrate the strands of the web to attract the female's attention. He may hang around the web for days before making his mood. Some species wait until the female is occupied with prey; others until she is about to moult. Some supply a prey item as a gift. In species with good eyesight such as the Lycosidae and Salticidae, the males signals his intentions with his legs and palps. Feigning death. 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. Moulting. Spiders moult their skins as many as 8 times before reaching adulthood. During the moulting process they can lose a leg, which will be regrown at the next moult.

Spiders and gardens

The Lycosidae will eat 5 - 15 small insects each day, and in California Pardosa ramulosa is an important predator of leafhoppers.
The Salticidae also have a fondness for leafhoppers and will eat 4 - 8 per day.
In China farmers build little straw huts beside their paddy fields for the spiders to overwinter in. In the UK money spiders protect the fields of winter wheat from aphids, and are active earlier in the year than ladybirds - another great aphid predator.
In France Tegenaria sp. are real eased into wine cellars as the presence of their webs is though to create feeling of age.
In Belgium many brewers believe that spiders are instrumental in controlling the numbers of fruit flies (Drosophilidae).

Amazing spider snippets

It has been estimated that in one year the weight of insects caught and eaten by spiders in the U. K. is equal to the weight of the entire human population. This also exceeds the weight of insects eaten by birds.

A hectare of meadow can contain over one million Linyphiidae (money spiders). This can be most easily seen when the webs are covered with the morning dew.

Spiders do not stick to their own webs because they either step on the non-sticky parts only, or secrete a special oil on their feet.

It is believed that spiders have been in existence for over 300 million years.

The largest spider that ever lived was Megarachne which lived during the Carboniferous and is now extinct. It was 33 cm long with a leg span of around 50 cm!

Agelenidae family. The general body shape (minus the legs) is shown in the drawing on the left. They have closely-woven webs with a silken tunnel attached where the spider rests and the female keeps her egg sac. The spider below left is a mature female Tegenaria sp., as her body was at least 2 cm I would guess that she is Tegenaria parietina. Tegenaria can have a leg-span of over 10 cm, though it is the males which have the really long legs. She had made her web inside a metal shed, and when I found her had grown too big to escape from the shed. She seemed quite happy living off a steady diet of insects though. Tegenaria are the big hairy spiders we commonly find wandering round out houses in autumn. Although we usually find males (right) as the females tend to stay on their webs. The males look very similar to the females except they are a few mm smaller in the body, have a thinner abdomen, longer legs and usually have swollen palps (see the photographs below right) as they are in search of a mate. Below left you can just make out the sclerotised entrance to the female's epigyne, this is the opening into which the male must place one of his sperm-charged palps. After a successful mating the males will usually live beside the females for a while, but die before winter, this provides the female with a substantial meal to see her through cold weather. Tegenaria can live for several years especially if they are in a sheltered location such as a house or closed metal shed. The webs can be pretty untidy, and often have a tubular retreat. On the left the female is on her web, note the long palps, these are always in contact with the web to detect any vibration indicating the presence of a possible snack. The spiderlings normally disperse without eating their mother.

The photographs on the right show a mature male Tegenaria duellica. Their body length is 10 - 14 mm long, and is slimmer than the females, although their legs are longer. Males mature in the late summer and autumn, and it is this time that you are most likely to find one wandering around your house. He is just looking for a mate. They are fairly widespread in Britain. They are found indoors, in outbuildings or sheltered walls in the north, but can survive outdoors in the south.

In 1760 when malaria, also known as ague, was common in Britain a Dr. Watson recommended a Tegenaria sp. "gently bruised and wrapped up in a raisin or spread upon bread and butter" as a cure !

In France Tegenaria sp. are released into wine cellars as the presence of their webs is though to create feeling of age.

In 1936 a policeman on point duty on Lambeth Bridge in London held up traffic to allow a particularly large Tegenaria parietina to cross the road.