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Life in Freshwater

Raft Spider (Dolomedes fimbriatus)

Raft Spider

This is a large, velvet, chocolate-brown spider with a white stripe along both sides of the body. It grows to become one of the largest European spiders with a body length of 22 mm in the female.

This is also known as a swamp spider because of its habitat of bog pools and fenland. It needs the permanent water for catching its prey and anywhere where there are pools and small ponds it can be found. It is widespread in Europe and fairly common in southern England .

ECOLOGY: The Raft Spider is found, typically, around the margins of bog pools although it can be found amongst damp grasses some way from water. It stands with the tips of the legs touching the surface of the water. Like a orb-weaving spider it has touch sensors on the legs which can detect vibrations. This raft spider uses them to pick up vibration on the surface tension of the water. An insect caught in the surface stimulates the sensors and the spider darts rapidly across the water to catch the prey. If the insect tries to escape it may be foiled by being struck by the spider's outstretched front legs, knocking it back into the water. They will even catch small fish that come to the surface. The spider normally spins a thread as it runs. This is a life-line, to find the way back to the water margin. The eyesight is poor in hunting spiders, used just for closeup. The velvet-like dense hairs on the body trap air, preventing it from sinking beneath the surface when it stops running. The female carries the large circular egg-sac under the body and then she has to run on the tips of her legs. Hibernation normally occurs in damp bog moss and the spider can live for up to five years.

See also Water Spider










Aranae - spiders


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