Dark Fishing Spider
Dolomedes tenebrosus
Pisauridae (Nursery Web Spiders), Order Araneae. Key characteristics include large size, cursorial hunting, and females carrying egg sacs in their chelicerae.
Physical Description
Large, robust spider with a flattened profile. The cephalothorax is broad with a distinct central groove. The abdomen is oval with fuzzy texture due to fine hairs. Females are significantly larger than males.
Size Estimate
Body length 15-26mm (females), 7-13mm (males). Leg span can reach 75-100mm (3-4 inches). This specimen looks to be an adult female.
Coloration & Markings
Mottled brown, gray, and black camouflage. Features three to four prominent W-shaped or chevron-like dark markings on the dorsal abdomen. The cephalothorax has a lighter tan U-shaped area near the eyes.
Web Type
None for hunting. They are active ambush predators. Females build a 'nursery web' of silk in vegetation only after the spiderlings begin to emerge from the egg sac.
Eye Arrangement
Eight eyes in two horizontal rows. The posterior row is strongly recurved, and the four posterior eyes are significantly larger than the anterior eyes, providing excellent motion detection.
Leg Characteristics
Long, thick, and powerful legs held in a flattened, sprawling posture. Legs feature prominent dark and light banding (annulations) and are covered in sensory hairs and small spines.
Venom & Safety Information
Venom Information
Contains neurotoxic components specialized for paralyzing invertebrate prey. For humans, the venom is not considered medically significant and is comparable to a bee sting.
Medical Significance
Low danger level. Harmless to healthy humans. Bites result in localized pain, redness, and minor swelling. Treatment involves cleaning the area and using ice for swelling.
Safety Recommendations
Relocate using a large container and a piece of cardboard if found indoors. Their size can be intimidating, but they are beneficial neighbors that keep larger pests in check.
Habitat & Behavior
Habitat & Range
Found throughout Eastern North America. Unlike other fishing spiders, this species is often found far from water in wooded areas, on tree trunks, rock faces, and frequently on the sides of houses or inside basements.
Behavior & Temperament
Active nocturnal hunters. They are fast and skittish, preferring to run and hide when disturbed. They are not aggressive toward humans and will only bite if pinned or handled roughly.
Diet & Prey
Generalist predators eating insects, other spiders, and occasionally small vertebrates like tadpoles. They use vibrations on surfaces to track prey and pounce with great speed.
Seasonal Activity
Most visible in late spring and summer during mating season. They often seek shelter in human structures during autumn to overwinter.
Description
A magnificent example of North American arachnid diversity, the Dark Fishing Spider is often mistaken for a wolf spider or even a tarantula due to its impressive size. Its intricate camouflage allows it to blend perfectly against bark or weathered wood.
Key Features
W-shaped abdominal markings, banded legs, flattened body posture, and typical Pisauridae eye arrangement. Distinct from wolf spiders by the lack of two extremely large top eyes.
Similar Species
Wolf spiders (Lycosidae) have different eye arrangements. Other Dolomedes species like D. triton are usually found closer to water and have white stripes on the sides.
Life Cycle
Females carry a large, spherical, tan egg sac in their jaws until they are ready to hatch. They then build a nursery web to protect the spiderlings. Lifespan is typically 1-2 years.
Ecological Importance
Vital apex predators within the micro-ecosystems of tree bark and forest floors. They provide significant natural pest control for large insects.
Conservation Status
Not evaluated by IUCN, but considered stable and common throughout its range. No immediate threats identified.
Interesting Facts
Despite their name, 'tenebrosus' means 'dark' or 'gloomy,' referring to their preferred shadowy habitats. They can run across the surface of water by utilizing surface tension.
Photography Tips
Focus on the eyes and the W-shaped markings on the abdomen. Use a side-angled shot to show their impressively flattened profile against the substrate.
Identified: 2026-07-10T22:28:58.005630