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Salticidae (jumping spiders) and Thomsidae (crab spider)

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This page - Salticidae - jumping spiders, Thomsidae - crab spiders

Stalticus sp. a jumping spider

Family Salticidae - jumping spiders.

There are 4000 species world wide, 75 in Europe, and 38 in Britain. The Northern European Salticidae are small and most commonly seen during warm sunny weather. The UK species have black and white, or brown and white stripes. They have the greatest visual acuity of all arthropods. Their eyes give them binocular vision and may be sensitive to colour and polarized light. The arrangement of eyes is shown on the right. The pair of small eyes furthest to the back

Salticul sp. a jumping spider, eye layout
the headlamp eyes of Salticus sp. a jumping spider

may just detect light and movement. The spider often rears up to get a better look at things, and they can spot prey 20 cm away. The pair of eyes between the 4 at the front and the two at the rear are hardly visible to the naked eye. The two large front-facing eyes are like headlamps (see left and right) and do reflect the light just like the eyes of a cat. They stalk prey then leap on it. They have a fondness for leafhoppers, and will eat 4 - 8 per day. Good vision os also needed during courtship. The male waves his legs and palps semaphore-style as he moves around the female trying to gauge if she is willing to mate. They have pads on their feet making it possible for them to cling to smooth surface - even glass.

Salticus sp. The most common species in the genus is Salticus senicus, commonly called the zebra spider because of its stripes. It is often found on walls, fences and window sills during warm, sunny weather. It's body length is 6 - 7 mm when fully grown. Greenfly are a favourite prey of this genus. It mates from May onwards.

Salticus sp. a jumping spider
Jumping spider with fly, Salticidae This photograph was taken on a wall in my garden. The movement of the fly attracted my attention, but I didn't see the spider at all as it was so well camouflaged. As you can see the fly is much bigger and heavier, but was already tiring. The spider just held on to the fly with its fangs and to the stone with its legs and drag line. It was totally oblivious to me, so I could get close enough to take this.
Thomsid spider, crab spider

Thomsidae - crab spiders

The spider on the left is a male of the Thomisidae family. There are 2 500 species world wide. It is easy to see he is a mature male because of his swollen palps. And also that he belongs to the Thomisidae family because his front two pairs of legs are longer than the rear pairs. Thomisids can live in a wide variety of habitats, and are often masters of camouflage. Some (mainly those which capture their prey while they lurk in flowers) even have the ability to change colour. They tend to sit and wait for their prey then make a quick grab with their first 2 pairs of legs, injecting a relatively powerful and quick-acting venom. Because of this method of prey capture none of them spin webs for ensnaring prey. They also have the ability of walking sideways which gives them their common name of crab spiders.

Curious courtship.
Some Thomsids, in the Xysticus genus such as X. lanio and X. cristatus, have a curious courtship. The male is slightly smaller than the female. He climbs over her body tying her down to the ground with numerous lines of silk. Then he pushes up her abdomen and squeezes underneath her to insert a sperm-loaded palp in her epigyne. However after this the female just gets up and walks away. The silk does not restrain her, so we do not yet know what is the purpose of the male tying her down.

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