Dark Fishing Spider, Northern Fishing Spider
Dolomedes tenebrosus
Pisauridae (Nursery Web Spiders), Order Araneae
Physical Description
Large, robust hunting spider with a flattened profile and long, powerful legs spread wide against surfaces. The cephalothorax features a broad central region with light lateral bands, and the abdomen is oval with W-shaped or chevron patterning.
Size Estimate
Female body length 15-26 mm, male body length 7-13 mm. Leg span can exceed 75-100 mm (3-4 inches) in adult females.
Coloration & Markings
Mottled brown, gray, and black coloration designed for camouflage against tree bark or rocks. Features distinctive dark chevron-shaped or W-shaped markings on the dorsal abdomen, bordered by lighter tan or white accents.
Web Type
Does not build prey-capture webs. Uses silk only for nursery webs built by females to protect egg sacs shortly before hatching.
Eye Arrangement
8 eyes arranged in two curved rows (4 in a slightly recurved anterior row, 4 larger eyes in a strongly recurved posterior row forming a wider line). Excellent vision for detecting movement.
Leg Characteristics
Long, thick, and highly muscular legs equipped with strong spines. Covered in fine hydrophobic hairs that allow them to walk on water surfaces.
Venom & Safety Information
Venom Information
Mild, non-necrotic, and non-neurotoxic venom designed to immobilize small invertebrate prey. Harmless to healthy humans.
Medical Significance
Not medically significant. Bites are rare and typically occur only when pinched or crushed against skin. Symptoms are comparable to a mild bee sting (localized pain, redness, mild swelling).
Safety Recommendations
No control measures are needed. If found inside a home, gently trap the spider using a plastic container and card, then release it outside near trees or outdoor structures.
Habitat & Behavior
Habitat & Range
Widespread across eastern and central North America. Inhabits wooded areas near water, tree trunks, rock faces, basements, and wooden structures such as docks, sheds, and porches.
Behavior & Temperament
Skittish, highly agile, and nocturnal ambush predator. Prefers to flee or flatten itself against substrate when threatened rather than bite. Extremely fast runner.
Diet & Prey
Generalist predator feeding on aquatic and terrestrial insects, moths, beetles, aquatic larvae, and occasionally small minnows or tadpoles caught near water margins.
Seasonal Activity
Most active from late spring through late summer. Adults mature in May-June, with nursery webs and egg sacs observed mid-to-late summer. Overwinters under loose bark or logs.
Description
The Dark Fishing Spider (Dolomedes tenebrosus) is one of the largest native spiders in eastern North America. Despite its name, this species is frequently found away from open water, hunting on forest trees, stone walls, and human-made structures. Its intricate brown and gray camouflage renders it nearly invisible when resting motionless on rough bark.
Key Features
Large size, mottled dark gray/brown bark camouflage, dark chevron markings on the abdomen, four light-colored cardiac marks or spots, and long stout legs held flattened against surfaces.
Similar Species
Dolomedes scriptus (striped fishing spider), Dolomedes triton (six-spotted fishing spider), and various large wolf spiders (Lycosidae family, which differ by eye arrangement and carrying egg sacs on spinnerets).
Life Cycle
Females carry a large spherical egg sac in their chelicerae. Before eggs hatch, the female constructs a silk nursery web among leaves or twigs and guards the spiderlings. Lifespan is typically 1 to 2 years.
Ecological Importance
Serves as an essential biological control for insect populations including beetles, mosquitoes, and flies, while providing food for birds, frogs, wasps, and small mammals.
Conservation Status
Not evaluated (IUCN), but widespread, common, and stable across its native geographic range.
Interesting Facts
Can walk on water by utilizing surface tension and hydrophobic leg hairs, and can even dive beneath the water surface to escape predators or catch aquatic prey.
Photography Tips
Use a diffuse flash or soft natural lighting to capture the fine surface textures and chevron patterns without overexposing reflective eye shines or dark camouflage gradients.
Identified: 2026-07-23T03:30:45.894811