Dark Fishing Spider
Dolomedes tenebrosus
Pisauridae (Nursery Web Spiders), Order Araneae
Physical Description
A large, robust spider with a flattened body profile adapted for hugging tree bark. The cephalothorax is broad with a distinct central groove, and the abdomen is elongated and tapered toward the rear. The body is covered in fine, velvet-like hairs.
Size Estimate
Large; females measure 15-26 mm in body length with a leg span often exceeding 75-100 mm (3-4 inches). This specimen appears to be a mature or sub-adult female.
Coloration & Markings
Mottled grey, brown, and black. Distinguished by dark, W-shaped or chevron markings on the abdomen and black ring-like bands on the legs. The cephalothorax often features a lighter-colored border or 'bracket' marks on the sides.
Web Type
The Dark Fishing Spider does not build a web for hunting; it is an active ambush predator. It only uses silk to construct egg sacs and 'nursery webs' to protect spiderlings after they hatch.
Eye Arrangement
Eight eyes in two horizontal rows. The bottom row has four small eyes, while the top row features four larger eyes arranged in a slightly recurved arc, providing excellent vision for detecting motion.
Leg Characteristics
Long, thick, and powerful legs held in a flattened, wide-reaching posture. The legs feature prominent dark banding (annulations) and are equipped with fine spines and sensory hairs (trichobothria).
Venom & Safety Information
Venom Information
Contains a variety of proteins and peptides designed to paralyze arthropod prey. It is not considered chemically dangerous to healthy humans and is less potent than that of a honeybee.
Medical Significance
Low medical significance. A bite may cause localized pain, redness, and swelling similar to a bee sting, typically resolving within a few days. No specific medical treatment is usually required unless an allergic reaction occurs.
Safety Recommendations
Encounters can be avoided by sealing cracks in basements and sheds. If found indoors, they can be safely relocated using the 'cup and cardboard' method. They should be appreciated at a distance to avoid triggering a flight response.
Habitat & Behavior
Habitat & Range
Common across Eastern North America, from Southern Canada to Florida and west to Texas. Unlike other fishing spiders, this species is frequently found far from water in wooded areas, on tree trunks, and inside sheds or basements.
Behavior & Temperament
A shy, nocturnal hunter that remains motionless during the day to blend into bark. They are extremely fast runners and will typically flee when disturbed. They are not aggressive toward humans and usually bite only if handled roughly.
Diet & Prey
Generalist predator feeding on a variety of large insects such as crickets, moths, and cockroaches. When near water, they may occasionally take small minnows or tadpoles using their front legs to sense vibrations on the surface.
Seasonal Activity
Most active from late spring through late summer. Mating occurs in early summer, and large females carrying egg sacs are frequently spotted in July and August.
Description
The Dark Fishing Spider is one of the largest spiders in North America. Despite its intimidating size and 'fishing spider' name, it is a master of camouflage frequently found in forests and near human structures. Its mottled pattern allows it to disappear against wooden surfaces.
Key Features
Large size, distinct W-shaped abdominal markings, black-banded legs, and a preference for vertical wooden surfaces rather than just water edges.
Similar Species
Often confused with Wolf Spiders (Lycosidae), but can be distinguished by eye arrangement and the lack of a single large pair of 'headlight' eyes. Also similar to Dolomedes scriptus, which has more distinct white edging on its markings.
Life Cycle
Females carry their large, globular egg sacs in their chelicerae (mouthparts) until the spiderlings are ready to hatch. They then build a nursery web in foliage. Life expectancy is typically two years, overwintering as immatures.
Ecological Importance
Significant apex invertebrate predator that helps control populations of large forest insects and provides a food source for birds, lizards, and small mammals.
Conservation Status
Not evaluated by IUCN, but considered common and widespread with stable populations throughout its range.
Interesting Facts
Despite their size, they can 'walk' on water using surface tension. They use their legs as tactile sensors to detect the wingbeats of nearby flies or the ripples of aquatic prey.
Photography Tips
Shoot from a side profile to capture the flattened body shape, or a top-down view to highlight the W-shaped markings. Use a moderate flash to bring out the subtle grey and brown textures against dark wood.
Identified: 2026-07-10T22:09:09.828146