Dark Fishing Spider, Dock Spider
Dolomedes tenebrosus
Pisauridae (Nursery Web Spiders), Order Araneae. Key family characteristics include distinct eye arrangements with two rows of curved eyes, the ability to walk on water surfaces, and females carrying their egg sacs in their chelicerae before constructing a tent-like nursery web.
Physical Description
Large, robust body with a distinct, rounded abdomen and broad cephalothorax. The body is covered in fine, velvety hairs providing excellent camouflage. The texture is matte rather than shiny, blending seamlessly into tree bark.
Size Estimate
Body length ranges from 15 to 26 mm for females (males are smaller, around 7 to 13 mm), with an impressive leg span reaching up to 70 to 90 mm. This specimen appears to be a mature or nearly mature individual.
Coloration & Markings
Mottled patterns of grey, brown, tan, and black providing exceptional cryptic camouflage. The abdomen features distinctive dark W-shaped or chevron markings alternating with lighter patches, while the legs are heavily banded.
Web Type
Fishing spiders do not spin webs to catch prey. Instead, they are active nocturnal or crepuscular hunters that roam over vertical surfaces, rocks, and near water. Females only spin a temporary nursery web of silk when their eggs are ready to hatch.
Eye Arrangement
Eight eyes arranged in two distinct, slightly curved rows. The eyes are dark and relatively uniform in size, characteristic of the Pisauridae family, giving them good forward-facing vision to detect movement.
Leg Characteristics
Long, powerful legs held out flat in a sprawling crab-like posture. The legs feature prominent spines, distinct dark banding, and are equipped with specialized hairs that repel water and allow the spider to glide across aquatic surfaces.
Venom & Safety Information
Venom Information
Neurotoxic and proteolytic venom used primarily to immobilize and digest prey. While potent enough to subdue small vertebrates, it is generally not dangerous to humans.
Medical Significance
Not medically significant. A bite from a dark fishing spider is rare and usually only occurs if the spider is trapped or squeezed against human skin. Symptoms are typically mild, comparable to a bee or wasp sting, involving localized pain, redness, and swelling.
Safety Recommendations
If found indoors, gently guide the spider into a container using a piece of cardstock and release it outdoors. If bitten, clean the area with soap and water and apply a cold compress. No special medical treatment is typically required.
Habitat & Behavior
Habitat & Range
Found throughout the eastern United States and parts of southeastern Canada. They inhabit wooded areas, frequently found on tree trunks, wooden fences, and near bodies of water such as streams, ponds, and docks.
Behavior & Temperament
Docile but fast-moving ambush and active hunter. They typically freeze when approached, relying on camouflage, or sprint rapidly toward safety rather than acting aggressively toward humans.
Diet & Prey
Generalist predators consuming large insects, aquatic invertebrates, small fish, and occasionally tadpoles. They detect prey vibrations on the water surface or land, rushing across the surface to grab and envenomate their catch.
Seasonal Activity
Most active from late spring through early autumn. They overwinter as juveniles or sub-adults under loose tree bark, in rotting logs, or beneath rock crevices.
Description
The Dark Fishing Spider is a magnificent giant among North American arachnids. With its sprawling posture, striking grey-and-brown mottled camouflage, and impressive leg span, it is an expert predator of both terrestrial and aquatic margins. Though intimidating due to its sheer size, it is a shy creature that plays a vital role in wetland and woodland ecosystems.
Key Features
Massive size, sprawling leg posture, mottled grey and brown coloration with chevron abdominal markings, and a strong preference for vertical tree trunks or structures near water rather than building traditional orb webs.
Similar Species
Wolf spiders (Lycosidae) can look very similar, but wolf spiders carry their egg sacs attached to their spinnerets and often have a distinct eye arrangement with two very large posterior median eyes. Other Dolomedes species like Dolomedes scriptus are also similar and distinguished by subtle carapace stripe patterns.
Life Cycle
Mating occurs in spring or early summer. Females produce a spherical silk egg sac, carrying it in their mouthparts. Just before hatching, she hangs the sac in vegetation and constructs a protective nursery web, guarding it fiercely until the spiderlings disperse.
Ecological Importance
Serves as a top invertebrate predator in riparian and woodland habitats, helping regulate insect populations and occasionally serving as a food source for birds, amphibians, and small mammals.
Conservation Status
Secure and widespread throughout its native range with stable populations. Not listed by the IUCN.
Interesting Facts
Despite being called fishing spiders, many individuals live far away from permanent water sources, roaming deep into deciduous forests where they hunt entirely on tree trunks.
Photography Tips
Use a macro lens with a fast shutter speed to capture the intricate leg banding and facial features. Shoot from a parallel angle to the body to keep the entire spider in focus, and use natural side-lighting to highlight its velvety texture.
Identified: 2026-10-02T23:16:38.367566