Dark Fishing Spider

Dolomedes tenebrosus is one of the largest North American spiders, with females spanning up to 90 mm across the legs and a 15–26 mm body mottled in brown, grey and black with distinctive chevron and W-shaped abdominal markings and banded legs. Females carry a large spherical egg sac of 500–1,000 eggs in their chelicerae, then build a nursery web in vegetation and stand guard until the spiderlings disperse. Development spans one to two years, with juveniles overwintering under bark and in crevices.

Despite the name, D. tenebrosus is the most terrestrial Dolomedes, often hunting well away from water on tree trunks and wooden structures. It builds no capture web, hunting by ambush and sensing prey vibration, and can run across water and submerge when threatened. Its size makes it alarming indoors, but it is retiring and flees; a defensive bite is possible if handled and produces local pain and swelling comparable to a bee sting with no lasting effect. Prey includes insects, slugs and occasionally small fish or tadpoles.