Dark Fishing Spider
Dolomedes tenebrosus
Pisauridae (Nursery Web Spiders), Order Araneae
Physical Description
A large, robust spider with a flattened body structure suited for clinging to tree bark and rock surfaces. The carapace features light-colored lateral margins, while the abdomen is elongated and oval. Dense micro-hairs coat the body and legs, providing water repelling capabilities.
Size Estimate
Estimated body length of 15-25 mm (excluding legs) with a total leg span reaching up to 75-100 mm (3-4 inches). Based on proportional leg length and body size, this specimen appears to be an adult or sub-adult.
Coloration & Markings
Variable gray to brownish-black base coloration with prominent light gray to beige bands. The abdomen exhibits distinct dark 'W' or chevron-shaped markings edged with white. Legs feature conspicuous alternating dark and light brown/gray annulations (stripes).
Web Type
Free-hunting spider that does not build capture webs. Females construct large silken nursery webs among foliage or structures to protect egg sacs shortly before spiderlings emerge.
Eye Arrangement
Eight eyes arranged in two curved rows. The anterior row is slightly recurved, while the posterior row is strongly recurved, forming a trapezoid pattern. Posterior eyes are moderately enlarged for keen motion detection.
Leg Characteristics
Long, thick, powerful legs equipped with prominent dark spines and dense scopula hairs that aid in gripping surfaces. Distinct alternating dark blackish-brown and light tan/gray banding spans all eight legs.
Venom & Safety Information
Venom Information
Contains general arachnid venom used to immobilize insect prey. The venom is not dangerous or medically significant to humans, comparable in effect to a mild bee sting.
Medical Significance
Low medical risk. Bites are rare due to their shy nature and occur almost exclusively when pinched or pressed against skin. Symptoms are limited to localized pain, minor swelling, and mild redness.
Safety Recommendations
Harmless to humans. If found indoors, safely capture using the cup-and-paper method and relocate to a nearby tree or wooded area outside.
Habitat & Behavior
Habitat & Range
Native to eastern North America, from southern Canada down to Florida and west to the Great Plains. Frequently found near water bodies, but uniquely adapted to dry wooded areas, tree trunks, basements, and wooden structures.
Behavior & Temperament
Active nocturnal ambush predator. Highly skittish and extremely fast runner, preferring flight over defense when startled. Although formidable in appearance, they are non-aggressive toward humans and retreat quickly.
Diet & Prey
Opportunistic predator feeding on aquatic and terrestrial insects, aquatic larvae, moths, beetles, and occasionally small vertebrates such as tadpoles or small fish if hunting near water.
Seasonal Activity
Most active from late spring through late summer. Adults mature in spring, mate, and females are commonly seen carrying egg sacs in June and July.
Description
The Dark Fishing Spider (Dolomedes tenebrosus) is one of North America's largest native spiders. Despite its common name, D. tenebrosus is frequently observed far from open water on tree trunks, stone walls, and wooden outbuildings. Its intricate camouflaged pattern provides superb concealment against mottled bark.
Key Features
Distinct W-shaped abdominal patterns, strongly striped/annulated legs, large size with flattened body posture, and light margins on the lateral carapace edges.
Similar Species
Dolomedes scriptus (Striped Fishing Spider, has continuous white chevrons), Dolomedes okefinokensis, and various Lycosidae (Wolf Spiders, which have much larger posterior median eyes and carry egg sacs attached to spinnerets).
Life Cycle
Females carry egg sacs using their chelicerae until eggs near hatching, at which point they build a nursery web in high vegetation. Females aggressively guard the web. Spiderlings disperse via ballooning or crawling; lifespan is 1 to 2 years.
Ecological Importance
Serves as an essential biological control agent for large insect populations like beetles, cockroaches, and moths, while serving as prey for birds, small mammals, and spider wasps.
Conservation Status
Not evaluated by IUCN, but widespread, common, and ecologically stable across its native distribution.
Interesting Facts
Despite frequenting dry land, they retain the ability to run across water surfaces, dive underwater, and trap air within their hydrophobic body hairs to breathe submerged.
Photography Tips
Approach slowly to avoid triggering their fast flight response. Use a side or top-down macro shot with good diffusion to capture the intricate leg banding and abdominal 'W' patterns without glare.
Identified: 2026-07-24T14:39:09.542704