Dark Fishing Spider, Dock Spider
Dolomedes tenebrosus
Pisauridae (Nursery Web Spiders), Order Araneae
Physical Description
Large, robust body with a flattened cephalothorax and elongated abdomen. Covered in fine setae giving it a velvety texture, showing exceptional camouflage against tree bark.
Size Estimate
Body length 15-26 mm, with a massive leg span reaching up to 70-90 mm. This appears to be a mature or near-mature adult.
Coloration & Markings
Mottled grayish-brown with dark alternating W-shaped chevrons and bands along the dorsal surface of the abdomen, providing remarkable disruptive cryptic coloration.
Web Type
Does not build a traditional capture web; instead, females construct a silken nursery web in vegetation prior to the hatching of their egg sacs.
Eye Arrangement
Eight eyes arranged in two curved rows, characteristic of Pisauridae, with anterior eyes generally equal in size to assist in active nocturnal foraging.
Leg Characteristics
Long, powerful legs held laterally in a sprawling crab-like posture. Spined and banded with dark rings, equipped with specialized claw tufts for walking on water surfaces.
Venom & Safety Information
Venom Information
Contains neurotoxic and proteolytic components designed for subduing invertebrate and small vertebrate prey; low potency regarding humans.
Medical Significance
Not medically significant. Bites are extremely rare, generally only occurring if the spider is trapped directly against bare skin. Symptoms are comparable to a mild bee sting.
Safety Recommendations
Observe from a distance. If found indoors, gently guide the spider into a container using a piece of cardstock and release it outdoors near a natural water source.
Habitat & Behavior
Habitat & Range
Found across eastern North America, typically inhabiting wooded areas near streams, ponds, swamps, and frequently found resting vertically on tree trunks or wooden docks.
Behavior & Temperament
Active nocturnal hunter with a timid disposition. When startled, they quickly flee to the other side of a tree trunk or dive beneath the water surface rather than confront threats.
Diet & Prey
Generalist predator feeding on large insects, tadpoles, small fish, and occasionally aquatic invertebrates detected via surface water vibrations.
Seasonal Activity
Most active from late spring through early autumn, mating in early summer, and overwintering under loose tree bark or inside sheltered crevices.
Description
The dark fishing spider is a master of camouflage, perfectly blending into the rough bark of trees where it spends much of its time. Despite its imposing size, it is a shy and beneficial giant of the riparian ecosystem, known for its ability to hunt both on land and across the surface of quiet waters.
Key Features
Large size, sprawling lateral leg posture, distinct W-shaped dorsal markings, and a preference for vertical tree surfaces near water.
Similar Species
Wolf Spiders (Lycosidae), which carry egg sacs attached to their spinnerets rather than in their jaws, and other Dolomedes species which share similar riparian habitats.
Life Cycle
Females carry round egg sacs in their chelicerae before attaching them to a vegetation nursery web. Spiderlings hatch within weeks, undergoing multiple molts to reach maturity over a 1-2 year lifespan.
Ecological Importance
Acts as an effective apex predator of the shoreline microhabitat, helping control insect populations and serving as food for larger amphibians and birds.
Conservation Status
Currently stable and not evaluated under IUCN Red List criteria; widely distributed with healthy populations across its native range.
Interesting Facts
Capable of remaining submerged underwater for up to an hour to evade predators, and can walk across the surface tension of water to capture small aquatic prey.
Photography Tips
Use natural side-lighting to highlight the intricate W-shaped abdominal patterns and maintain a respectful distance to avoid startling the spider into fleeing.
Identified: 2026-09-08T20:10:16.525425