Sunday, 4 October 2015

Scytodidae: Spitting spiders

Spitting spiders are a small family, with just one British species, Scytodes thoracica. They are small (3-6 mm, female larger than the male) but easily recognisable with a dark markings like line drawings over paler background and clearly annulated legs. In the UK the spitting spider lives inside buildings, mainly in the south. It is a nocturnal wandering hunter, which does not build a web, and can be encountered prowling on walls. It has six eyes, with a characteristic arrangement. Males and females are very similar, and both the female genital opening and male palps are simple.

A glue shooting spider
The common name of Scytodidae comes from their unique method of capturing prey. They have a relatively large domed cephalothorax, larger than its abdomen, which holds paired glands which produce both poison and a glue-like substance containing silk. The glands open in the fangs and the spider is able to aim at potential prey at distance and shoot a mixture of glue and venom while swaying the fangs. The resulting paired zigzag pattern of gluey-silk strands entangles the prey and attaches it to the ground. The spider also uses its squirting action against other spiders larger than themselves.

Spitting spiders make a simple egg sac. The eggs are large, and each batch contains 20-35. The female holds the egg sac with her palps and spinnerets, and can feed while carrying the eggs. The spiderlings emerge from the egg sac, and hang from a web the mother builds from them. After about 10 days, the moult and disperse. They are slow developers, and long lived for such small spider, females mature at two to three years old and can live up to five years.

Scytodes thoracica on a wall
Feigning death when disturbed.
Face on view.

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