Last updated on April 19, 2014 at 9:20 EDT

Tetragnatha extensa

Tetragnatha extensa is a species of spider found across the Northern Hemisphere. It has an elongate body, up to .43 inches long, and assumes a straight line posture when it is alarmed. It lives on low vegetation in damp areas and consumes flying insects which it catches in its web.

This spider has a stretched out, cream colored body. The males are smaller than the females at around .35 inches body length, compared to .43 inches in the females. The four pairs of legs are long and a dark yellow color. The carapace, which is about 1.8 to 2.6 millimeters long and 1.1 to 1.7 millimeters wide, is orange or dark yellow in coloration.

It has a wide distribution across the Northern Hemisphere. In North America, it can be found from Alaska to Newfoundland, and its range extends south to Washington, Colorado, and Pennsylvania. The species has a broad ecological range, having been found at the tree line in the Rocky Mountains and in coastal vegetation in Europe. It can be found throughout the United Kingdom, where it is the most common species of Tetragnatha, and one of the most common spiders. The coloration of this spider is rather variable, ranging from creamy yellow to green. On the underside, there is a thick black colored central band with a silvery band on either side.

It can be distinguished from other members of the genus Tetragnatha by the tiny curved tip of the male’s conductor, and the form of the female’s spermatheca.

T. extensa is found on low-growing vegetation, normally in damp areas. It consumes insects, including mosquitoes, moths, and midges, which it catches in its loosely-built web. When it is alarmed, it will sit along a plant stem, a blade of grass or the central vein of a leaf, with its four front legs pointing forwards, and its four back legs pointing backwards for camouflage. It is able to walk on the surface of water, where it can move faster than on land.

The adults are seen between May and September within the United Kingdom, and between may and July within Alaska. There is little courtship, and the male and female lock jaws, probably to prevent the female from eating the male before mating. The egg sacs are spherical and covered with grey tufted silk, looking much like a bird dropping, and are pressed against a plant stem. Overwintering occurs in the form of early-instar spiderlings.

This species was initially given a binomial by Carl Linnaeus in his Systema Naturae of 1758, the starting point of zoological nomenclature.

Image Caption: Tetragnatha extensa web, from Commanster, Belgian High Ardennes. Credit: James K. Lindsey/Wikipedia (CC BY-SA 2.5)

Tetragnatha extensa