Dark Fishing Spider
Dolomedes tenebrosus
Pisauridae (Nursery Web Spiders), Order Araneae
Physical Description
Large, flattened body with a mottled, lichen-like texture. Cephalothorax features a lighter central area bordered by dark bands and light margins. The oval abdomen is broad, slightly flattened, and tapers towards the rear with distinct light W-shaped markings or chevrons.
Size Estimate
Body length is approximately 15-25 mm (0.6-1.0 inch) for adult females, with a leg span often reaching 75 mm (3 inches) or more. Males are significantly smaller. This specimen appears to be an adult female based on body proportions.
Coloration & Markings
Mottled brown, gray, and black overall, providing exceptional camouflage against tree bark and weathered wood. Features distinct dark W-shaped or chevron markings bordered by white or pale gray accents running down the dorsal abdomen. Legs display prominent dark and light alternating bands.
Web Type
Does not construct capture webs for hunting. Females build a nursery web made of silk wrapped around surrounding foliage or structures specifically to protect their egg sac and newly hatched spiderlings.
Eye Arrangement
Eight eyes arranged in two curved rows. The lower row consists of four smaller eyes, while the upper row features four larger eyes, giving them keen vision adapted for active hunting.
Leg Characteristics
Long, robust legs covered in fine, erect macrosetae (spines) and hairs. Legs display distinct dark and light banding. Equipped with specialized hairs (scopulae) that allow them to grip smooth surfaces and run across the surface film of water.
Venom & Safety Information
Venom Information
Contains mild, complex venom designed to quickly immobilize small invertebrate prey. Venom is non-necrotic and not neurotoxic to humans.
Medical Significance
Harmless to humans. Bites are rare and medically insignificant, comparable to a mild bee or wasp sting with localized pain, slight swelling, and minor redness that subsides quickly.
Safety Recommendations
If found indoors or on a home deck, relocate gently using the cup-and-cardboard method. Wear gloves if handling woodpiles or dark sheds where they like to hide. Bites require only basic soap-and-water washing and an ice pack if swelling occurs.
Habitat & Behavior
Habitat & Range
Widespread across eastern North America, from southern Canada down to Florida and west to Texas and the Midwest. Commonly found on tree trunks, rock faces, wooden fences, decks, and human structures, often near wooded areas, streams, or lakes, though D. tenebrosus ranges farther from open water than other fishing spiders.
Behavior & Temperament
Active nocturnal ambush hunter with excellent vision and sensitivity to vibrations. Shy, skittish, and extremely quick to flee when approached or threatened. Non-aggressive towards humans and will bite only if pinned or squeezed against skin.
Diet & Prey
Opportunistic predator feeding on a wide variety of insects, moths, aquatic larvae, and occasionally small vertebrates like tadpoles or small fish if near water. Captures prey by pouncing with impressive speed.
Seasonal Activity
Most active from late spring through early autumn. Females carrying egg sacs or guarding nursery webs are frequently spotted in June and July.
Description
The Dark Fishing Spider (Dolomedes tenebrosus) is one of North America's largest native spiders. Despite its formidable size and tiger-striped appearance, it is a harmless, beneficial predator that excels at blending seamlessly into tree bark, wooden structures, and forest floors.
Key Features
Large size with broad leg span; prominent dark and light banding on legs; distinct dorsal abdomen pattern of pale W-shaped chevrons outlined in black; mottled gray-brown cryptically colored body.
Similar Species
Dolomedes scriptus (Striped Fishing Spider), Dolomedes triton (Six-spotted Fishing Spider), and various Wolf Spiders (Lycosidae family). Distinguished from wolf spiders by eye arrangement and lack of a large central pair of eyes, and from D. scriptus by the distinct W-shapes on the abdomen rather than continuous pale bands.
Life Cycle
Females produce a large, round brownish egg sac in early summer, carrying it under their prosoma with their chelicerae. Before eggs hatch, the female constructs a nursery web and guards it aggressively. Spiderlings disperse via ballooning or crawling; lifespan is typically 1 to 2 years.
Ecological Importance
Serves as an essential natural biological control for populations of nocturnal insects, crop pests, and wood-boring insects. Also serves as a food source for birds, small mammals, and predatory wasps.
Conservation Status
Not evaluated by the IUCN; widespread, common, and stable across its native range with no immediate conservation threats.
Interesting Facts
Despite their common name, Dark Fishing Spiders are often found far away from standing water in dry hardwood forests, home decks, and sheds. They can walk on the surface of water using surface tension and submerge briefly to catch prey or escape predators.
Photography Tips
Capture the full dorsal pattern from directly above to highlight abdomen chevrons and leg banding. Use a ring light or diffused flash to avoid harsh shadows and emphasize the velvety hair texture.
Identified: 2026-07-27T21:04:20.735654