Dock spiders, also known as fishing spiders, wharf spiders, or raft spiders, are large arachnids commonly found in North America. They are often encountered near bodies of water, which gives them their common names. Understanding their physical traits, behaviors, and the nature of their bites can help alleviate common concerns.
Physical Characteristics and Identification
Dock spiders are among the largest spiders in North America. Female body lengths range from 15 to 26 millimeters, with males typically half that size. Including their long legs, a female can measure up to 100 millimeters (about 4 inches). Their coloration is typically brownish-grey, often featuring black and brown markings on their abdomens and striped patterns on their legs.
These spiders possess eight eyes arranged in two rows. Their hairy bodies and legs are covered in water-repelling hairs, essential for their semi-aquatic lifestyle. Females are significantly larger than males.
Natural Habitat and Behavior
Dock spiders belong to the genus Dolomedes and are predominantly found in aquatic or semi-aquatic environments, such as near docks, ponds, lakes, rivers, and streams. They often hide among rocks, vegetation, or debris along shorelines. While primarily associated with water, they can also be found in boathouses, on boats, and occasionally wander into nearby homes.
These spiders are unique for their ability to walk and run across the surface of water, utilizing surface tension and their specialized water-repelling leg hairs. They are active hunters and do not construct webs to capture prey.
Instead, they position themselves at the water’s edge, resting their front legs on the surface to detect vibrations from potential prey like aquatic insects, small fish, and tadpoles. When a target is detected, they rapidly move across the water to subdue it. They can even dive underwater for extended periods, sometimes up to 45 minutes, by trapping air within the hairs on their bodies.
Understanding Dock Spider Bites and Venom
Dock spiders possess venom, but it is generally considered mild and not medically significant to humans. Their venom is primarily used to subdue prey. Bites from dock spiders are rare, typically occurring only when the spider feels threatened, is accidentally trapped against skin, or is handled.
When a bite occurs, symptoms are usually localized and minor, often described as similar to a bee sting. Common reactions include mild pain, localized redness, and some swelling at the bite site. These symptoms typically subside within a few days without requiring medical intervention.
While severe allergic reactions are uncommon, individuals with a history of severe reactions to insect bites should exercise caution. Dock spiders are not aggressive and prefer to flee when disturbed.