Dark Fishing Spider
Dolomedes tenebrosus
Pisauridae (Nursery Web Spiders), Order Araneae
Physical Description
A large, robust spider with a flattened body profile and a somewhat oval abdomen. The cephalothorax is broad and powerful. Their bodies are covered in fine, velvety hairs that provide some water resistance. This specimen appears to be a female, as they are significantly larger than males.
Size Estimate
Body length 15-26mm for females; leg span can reach 75-100mm (3-4 inches). Based on the image context, this is a large adult female.
Coloration & Markings
Highly camouflaged with a base color of grey to brown. Features characteristic dark, W-shaped or chevron-like markings on the abdomen and dark ring-like bands (annulations) on the legs. The cephalothorax often has a light-colored margin or 'U' shaped pattern behind the eyes.
Web Type
They do not build webs for hunting. They are active pursuit hunters. Females only build a 'nursery web' to protect their egg sac just before the spiderlings hatch.
Eye Arrangement
Eight eyes arranged in two rows. The posterior row is slightly recurved (curving backwards) and larger than the anterior row. This arrangement provides excellent vision for detecting movement at a distance.
Leg Characteristics
Long, thick, and powerful legs designed for sprinting. They are distinctly banded with dark and light stripes. The legs have prominent spines (macrosetae) and are held in a wide, sprawling posture that distributes weight effectively across surfaces.
Venom & Safety Information
Venom Information
Contains complex proteins and neurotoxins primarily effective against arthropods. For humans, the venom is not considered medically significant and is comparable to a bee sting in potency.
Medical Significance
Low danger level. Harmless to healthy humans. Bites may cause localized pain, redness, and swelling similar to a wasp sting. Treatment involves cleaning the site and applying a cold compress. Seek medical attention only if an allergic reaction occurs.
Safety Recommendations
If found indoors, use the 'cup and card' method to safely relocate the spider outside to a tree or wooded area. Wear gloves if you are nervous, but remember they are not interested in biting. To prevent entry, seal cracks in foundations and ensure window screens are tight.
Habitat & Behavior
Habitat & Range
Common across Eastern and Central North America. While called 'fishing spiders', this specific species (tenebrosus) is often found far from water in wooded areas, on tree trunks, or inside basements and garages.
Behavior & Temperament
An ambush and pursuit predator. They are incredibly fast and can run across water surfaces or vertically up walls. Generally shy and will flee rapidly when disturbed. They are not aggressive toward humans and usually bite only if trapped against skin.
Diet & Prey
Generalist predators eating a wide variety of insects, other spiders, and occasionally small vertebrates like minnows or tadpoles if near water. They hunt by sensing vibrations through their legs.
Seasonal Activity
Most active from late spring through late summer. Females carrying egg sacs are most frequently spotted in July and August. They remain dormant during the coldest winter months.
Description
The Dark Fishing Spider is one of the largest spiders found in North America. Despite its name, it is frequently encountered in dry habitats such as wooded sheds, basements, and on forest floors where its mottled grey pattern provides perfect camouflage against bark and stone. It is a wandering giant that relies on speed and vibration sensing rather than silk traps to secure its meals.
Key Features
Large size (3+ inch leg span), distinct dark W-shaped abdominal markings, prominent dark banding on legs, and the absence of a capture web.
Similar Species
Dolomedes scriptus looks very similar but is more strictly aquatic. Wolf Spiders (Lycosidae) are often confused with them but have a different eye arrangement (two very large eyes in the middle row) and carry egg sacs attached to their spinnerets rather than in their mouths.
Life Cycle
Females carry their large silken egg sacs in their chelicerae (mouthparts). Before hatching, they construct a nursery web and guard it. Spiderlings may disperse via 'ballooning' on silk threads. They can live up to two years, overwintering as juveniles in sheltered bark or crevices.
Ecological Importance
Crucial apex invertebrate predators. They provide significant natural pest control by consuming large numbers of insects. They also serve as a food source for birds, lizards, and small mammals.
Conservation Status
Not evaluated by the IUCN, but considered common and stable throughout its range. Their primary threat is habitat loss and the indiscriminate use of pesticides in residential areas.
Interesting Facts
They can skate across the surface of water using surface tension and can even dive underwater, trapping a thin layer of air against their bodies to breathe. They are remarkably fast, capable of covering several feet in a second when startled.
Photography Tips
Focus on the cephalothorax to capture the eye arrangement for identification. Use a side-angled light to highlight the texture of the markings. Maintain a respectful distance; if the spider tucks its legs in tight, it is stressed.
Identified: 2026-07-05T23:49:58.214546