Dark Fishing Spider, Dock Spider
Dolomedes tenebrosus
Pisauridae (Nursery Web Spiders), Order Araneae
Physical Description
Large, robust body with a distinctively patterned cephalothorax and elongated abdomen. Females are notably larger than males, displaying typical sexual dimorphism for this genus. The body is covered in fine setae giving it a slightly velvety texture.
Size Estimate
Body length ranges from 15 to 26 mm for females, with a leg span that can reach up to 70 to 90 mm (approx. 3 inches), making it one of the largest spiders in its range.
Coloration & Markings
Mottled brown, gray, and black coloration designed for camouflage against tree bark. The cephalothorax features pale longitudinal stripes, and the abdomen has distinctive dark W-shaped or chevron markings.
Web Type
Does not build a web to catch prey. Females construct a prominent spherical silken nursery web in vegetation when guarding their egg sacs, but otherwise rely on active hunting.
Eye Arrangement
Eight eyes arranged in two distinct curved rows, typical of the family Pisauridae, with eyes being relatively equal in size compared to wolf spiders whose posterior median eyes are much larger.
Leg Characteristics
Long, powerful legs held out flat in a sprawling crab-like posture when resting. Legs feature dark bands and prominent spines, well-adapted for running rapidly across vertical surfaces and water.
Venom & Safety Information
Venom Information
Neurotoxic and proteolytic venom designed to immobilize arthropod prey. Not medically significant to humans, though a defensive bite can cause localized pain, swelling, and redness similar to a wasp sting.
Medical Significance
Harmless to humans. Bites are rare and only occur when the spider is directly trapped, handled, or when a nesting female is threatened. Symptoms are typically mild and resolve on their own without medical intervention.
Safety Recommendations
Avoid handling them bare-handed. If found indoors, they can be easily safely relocated outside using a container and a piece of cardboard. No pest control measures are necessary as they are beneficial predators.
Habitat & Behavior
Habitat & Range
Found throughout eastern North America, typically inhabiting wooded areas near streams, ponds, and wetlands, but frequently encountered on the walls of houses, barns, and fences far from water.
Behavior & Temperament
Nocturnal hunter that actively ambushes prey. Generally non-aggressive toward humans, preferring to flee or hide when disturbed, though brooding females guarding nursery webs may defend their egg sacs.
Diet & Prey
Primarily feeds on insects, but capable of subduing small aquatic prey including tadpoles, small fish, and aquatic insects by utilizing vibrations on the water surface.
Seasonal Activity
Most active during the warm spring and summer months. Mating typically occurs in late spring or early summer, and they overwinter under loose bark, in hollow trees, or occasionally inside outbuildings.
Description
The Dark Fishing Spider is an impressive and agile hunter often found far from its typical aquatic habitats on wooden structures and tree trunks. With its striking camouflage, sprawling stance, and formidable size, it commands attention as one of the forest's stealthy nocturnal predators.
Key Features
Large size, pale stripes on the cephalothorax, dark W-shaped chevrons on the abdomen, and a sprawling leg posture without a traditional orb or sheet web.
Similar Species
Wolf spiders (Family Lycosidae), which can be distinguished by their eye arrangement (particularly the large posterior median eyes) and the habit of female wolf spiders carrying egg sacs attached to their spinnerets rather than in their jaws.
Life Cycle
Females carry their large spherical egg sacs in their jaws until just before hatching, then construct a silken nursery web in leaves or under bark. Spiderlings hatch within the web and disperse after a few molts. Lifespan typically spans up to two years.
Ecological Importance
Acts as an important generalist predator helping to regulate insect populations and occasionally small aquatic organisms, serving as a vital link in both terrestrial and aquatic food webs.
Conservation Status
Not evaluated by the IUCN, but populations are generally stable and widespread throughout their native range with no major conservation threats.
Interesting Facts
Despite being called fishing spiders, many individuals live miles away from permanent water bodies. They can walk on the surface of water using surface tension and can even submerge themselves briefly to escape predators.
Photography Tips
Use a macro lens and a diffuser for your flash to minimize harsh reflections on the spider's carapace. Approach slowly to avoid startling them into fleeing, and photograph from a parallel angle to capture the distinct dorsal markings.
Identified: 2026-10-13T20:56:08.921355