Dark Fishing Spider
Dolomedes tenebrosus
Pisauridae (Nursery Web Spiders), Order Araneae. Key family traits: large size, ability to run on water, and maternal care including carrying the egg sac by the chelicerae.
Physical Description
A large, robust spider with a flattened body profile adapted for hugging tree bark. It features a broad cephalothorax and an oval-shaped abdomen. The body is densely covered in fine, short hairs (pubescence) giving it a velvety texture, crucial for camouflage and surface tension on water.
Size Estimate
Large; body length typically 15-26mm for females and 7-13mm for males. Total leg span can reach 75-100mm (3-4 inches). This specimen appears to be an adult female based on its size and proportions.
Coloration & Markings
Mottled brown, gray, and black coloration designed for camouflage on tree bark. The cephalothorax features pale U-shaped markings. The abdomen has several dark, W-shaped or chevron-like marks along the dorsal midline. Legs are heavily banded with dark rings.
Web Type
This is a hunting spider that does not spin a web for prey capture. However, females construct 'nursery webs'—a protective silk tent amidst foliage to house spiderlings after they emerge from the egg sac.
Eye Arrangement
Eight eyes in two rows. The posterior row is slightly curved and contains larger eyes than the anterior row. This arrangement provides excellent vision for spotting movement from several inches away.
Leg Characteristics
Long, thick, and powerful legs held in a flattened, wide-reaching stance. They are equipped with numerous spines (macrosetae) and are distinctly banded with dark and light brown rings. They lack the specialized 'comb' of cobweb spiders.
Venom & Safety Information
Venom Information
Contains neurotoxic components designed to paralyze insects. The venom is not considered medically significant for healthy humans, though it is potent enough to subdue prey larger than itself.
Medical Significance
Low danger level. Bites are rare and comparable to a bee sting in severity, involving localized pain, redness, and minor swelling. No special medical treatment is usually required unless an allergic reaction occurs.
Safety Recommendations
No action is needed as they are harmless to humans. If one must be moved from a home, use a large container (like a quart-sized bowl) and a piece of cardboard to scoop it up and release it near a tree or woodpile.
Habitat & Behavior
Habitat & Range
Found throughout the Eastern United States and Southern Canada. Despite the name 'fishing spider,' this specific species is frequently found far from water in wooded areas, on vertical surfaces like tree trunks, and common on man-made structures like the deck/sliding seen here.
Behavior & Temperament
An ambush predator that waits motionless for prey. They are incredibly fast runners and can be skittish, usually choosing to bolt rather than defend themselves. They are not aggressive toward humans and will only bite if pinned or handled roughly.
Diet & Prey
Opportunistic hunters. Diet includes large insects like crickets, moths, and cockroaches. When near water, they can occasionally catch small fish or tadpoles, but D. tenebrosus feeds primarily on terrestrial arthropods.
Seasonal Activity
Emerge as juveniles in early spring and reach maturity by early summer. Most active and visible from May through September. Overwinters as a sub-adult in sheltered crevices.
Description
The Dark Fishing Spider is one of the most impressively large spiders found in North America. Its intricate gray and brown patterning allows it to vanish against wooden surfaces or stone. Unlike most of its cousins who stick to the water's edge, this species is a frequent visitor to backyard decks and suburban homes.
Key Features
Distinguished by its massive size (up to 4 inches leg span), distinct W-shaped abdominal markings, banded legs, and the habit of resting flat against vertical wooden or stone surfaces.
Similar Species
Often confused with Wolf Spiders (Lycosidae), but can be distinguished by the eye arrangement and the fact that Wolf Spiders carry egg sacs on their spinnerets, not their mouthparts. It also resembles the White-banded Fishing Spider (D. albineus).
Life Cycle
Females carry their large, round, silk egg sacs in their chelicerae (mouthparts). Before the eggs hatch, she builds a nursery web and guards it. Spiderlings may disperse via ballooning. The lifespan is typically 1-2 years.
Ecological Importance
Significant apex invertebrate predator. They provide excellent natural pest control by eating cockroaches, crickets, and other large insects that may invade homes or gardens.
Conservation Status
Not evaluated by the IUCN, but considered common and stable throughout its range with no major threats.
Interesting Facts
Despite being a 'fishing' spider, D. tenebrosus is the most terrestrial of the genus. They are capable of 'sailing' across water surfaces using their legs as sails and the wind for propulsion.
Photography Tips
Since they are very flat, a direct 'top-down' bird’s-eye view is best for showing the abdominal chevrons. Use a macro lens from a distance to avoid startling the spider, as they are very sensitive to vibrations.
Identified: 2026-05-31T23:33:31.118094