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Stephanopis pustulosa D6957
There is just a single species in Britain belonging to the genus Misumena. As the common name suggests, it is reminiscent of a crab, with its wide, flattened body form and habit of sitting with the first pair of legs held apart. This spider has the remarkable ability to alter its colour to match its background, usually a white or yellow flower, allowing it to become beautifully camouflaged. The sexes are different in appearance; females vary in color from white to pale green or yellow, depending on the background. They tend to have two pairs of bright red spots on the abdomen, but these may be fused to form red lines or even entirely missing. Males are much smaller in size than females and have more slender greenish white abdomens that feature brown stripes.

Biology Edit

This species does not spin a web to catch its prey. Instead it lies in wait on flowers and vegetation for a suitable prey species to visit and swiftly ambushes the insect. It then injects venom into the prey with the slender fangs. Males deposit a drop of sperm which is taken up by specialised leg-like appendages known as ‘palps’. During copulation, the sperm is passed to the female’s reproductive organ (the ‘epigyne’). After mating, the female lays the eggs, folds a leaf over them and spins a protective silk cocoon around the folded leaf. She will then cease to feed and stands guard over the eggs for around three weeks, after which the eggs hatch and the female dies.

Range Edit

In Britain, this spider is found mainly in southern England. It is also found throughout much of mainland Europe, North America and South America.

Behavior Edit

Thomisidae do not build webs to trap prey, though all of them produce silk for drop lines and sundry reproductive purposes; some are wandering hunters and the most widely known are ambush predators. Some species sit on or beside flowers or fruit, where they grab visiting insects. Individuals of some species, such as Misumena vatia, are able to change color over a period of some days, to match the flower on which they are sitting. Some species frequent promising positions among leaves or bark, where they await prey, and some of them sit in the open, where they are startlingly good mimics of bird droppings. However, these members of the family Thomisidae are not to be confused with the spiders that generally are called bird-dropping spiders, not all of which are close relatives of crab spiders.

Other species of crab spiders with flattened bodies either hunt in the crevices of tree trunks or under loose bark, or shelter under such crevices by day, and come out at night to hunt. Members of the genus Xysticus hunt in the leaf litter on the ground. In each case, crab spiders use their powerful front legs to grab and hold on to prey while paralysing it with a venomous bite. The spider family Aphantochilidae was incorporated into the Thomisidae in the late 1980s. Aphantochilus species mimic Cephalotes ants, on which they prey.

The spiders of Thomisidae are not known to be harmful to humans. However, spiders of an unrelated genus, Sicarius, which are sometimes referred to as "crab spiders", or "six-eyed crab spiders", are close cousins to the recluse spiders, and are highly venomous, though human bites are rare.

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