Sunday, 11 October 2015

Tetragnathidae: stretch spiders or long-jawed orb weavers

This is a large world family, with only 14 British species. Most build orb webs and sit in the middle, instead of having a signal thread and a retreat as in typical orb weavers (Araneae). Tetragnatha are very elongated spiders with slender bodies and long legs, except the third pair, which is short and often hold the spider to stems and grasses while the remaining pairs are stretched forward and back. When disturbed, they run out of their web and stretch themselves along leaves or stems. Some species have a preference for damp places and one of them Meta menardi, lives in caves and other dark places. One of the genera, Pachygnatha, does not build webs when adults.

The locking of the jaws
Males and females have extremely long chelicers furnished with internal spines. Males have two pair of additional large and spines protruding from the inside and outside of his chelicers. These spines lock the female's chelicers open during mating. The male's palps are also very long. For a video of a mating pair of Tetragnatha click here and for a fantastic post by Catherine Scott with observations of mating and male competition click here.

Tetragnatha extensa on resting posture on a leaf over the pond water.
Tetragnatha extensa turning on a leaf allowing to see her chelicers.
Tetragnatha extensa on her web over a pond
Female Metellina sp. on her web. Metellina females are quite plump and don't have particularly long legs.
Male Metellina guarding a female's web. Unlike the female, he is slender and looks more similar to Tetragnatha. He will wait until a female catches an insect to mate. For more information on this species mating strategy see this post at Bugblog.

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