Overview
The Dark Fishing Spider (Dolomedes tenebrosus) is an impressive, titanic arachnid that reigns as one of the largest native spiders in eastern North America. Boasting a formidable leg span that can reach five inches across, this handsome, velvety giant is famous for its intricate, bark-like camouflage and its surprising terrestrial lifestyle, often found hunting far from water on the vertical trunks of giant oak and maple trees.
Biology and Physical Characteristics
Dolomedes tenebrosus possesses a broad, flattened cephalothorax and abdomen colored in an intricate, mottled mosaic of slate-grey, rich chocolate-brown, and black, accented by distinct W-shaped or chevron markings down the back. Its long, muscular legs are heavily banded in black and tan and densely covered in sensory hairs (trichobothria) that detect the faintest vibrations. Despite its formidable size and venomous fangs, it is completely harmless to humans.
Behavior and Ecology
Unlike its strictly semi-aquatic cousins that float on open water, the Dark Fishing Spider is predominantly a forest-dwelling tree-hunter. Strictly nocturnal, it spends daylight hours flattened motionless against rough tree bark, becoming virtually invisible. At night, it hunts actively along tree trunks and rock faces, capturing large moths, tree crickets, and occasional tree frogs with explosive athletic lunges.
Conservation and Human Impact
Widely distributed and abundant throughout eastern North American forests, Dolomedes tenebrosus frequently encounters humans when it wanders into rustic lakeside cabins, boathouses, and wooden sheds in late summer. It serves as a vital predator of large woodland insects and a nutritious food source for forest birds and predatory pompilid wasps.
Interesting Factoid
Despite being called a ‘fishing spider,’ the Dark Fishing Spider often lives deep in dry oak forests hundreds of yards from any water, spending its nights climbing giant trees and sprinting down trunks to tackle woodland moths.