Dock spiders, also known as fishing spiders or wharf spiders, are fascinating arachnids often found near bodies of water. Their size and unique behaviors often spark curiosity and apprehension. These spiders possess remarkable adaptations that allow them to thrive in semi-aquatic environments, distinguishing them from many other spider species. Understanding them helps demystify their presence and highlights their ecosystem role.
Identifying Dock Spiders
Dock spiders are known for their size; adult females often reach a body length of 15 to 26 millimeters, not including their legs. With legs extended, females can span up to 10 centimeters, roughly the size of an adult human hand. Males are typically smaller, averaging between 8 and 13 millimeters in body length. Their coloration generally ranges from brownish-grey, featuring black and light brown markings on their abdomens.
Their eight widely spaced, striped legs are covered in water-repelling hairs. These specialized hairs, called scopulae, help them navigate water surfaces. Unlike some other large spiders like wolf spiders, dock spiders possess two rows of eyes, a feature that helps differentiate them. Their robust bodies and long legs suit them for agility and strength.
Where Dock Spiders Live and Hunt
Dock spiders are predominantly found in areas with abundant water sources, such as lakes, rivers, marshes, and ponds. They prefer wetland habitats due to available food and shelter, often along shorelines with dense vegetation or structures like docks and boathouses. While typically associated with water, they also inhabit forests, under rocks, or tall plants. They may seek indoor shelter in cottages or boathouses as colder weather approaches.
These spiders do not spin webs to catch prey, a common misconception. Instead, they are active hunters, relying on their ability to detect vibrations on the water’s surface. A dock spider often rests its front legs on the water, feeling for ripples from insects, tadpoles, or small fish. Once prey is detected, they rapidly run across the water to attack.
Dock spiders can dive underwater and remain submerged for several minutes, sometimes up to 45 minutes, by trapping air bubbles. Their diet includes aquatic insects, minnows, frogs, and tadpoles; they can subdue prey significantly larger than themselves.
Dock Spiders and Humans
Despite their size, dock spiders are not aggressive towards humans. They avoid confrontation, typically retreating or freezing if threatened. Bites are rare, occurring only when the spider feels cornered, is handled, or accidentally trapped (e.g., inside clothing).
Their venom is primarily for subduing natural prey and is not highly significant to humans. A bite is often compared to a bee sting, causing localized pain, redness, and swelling that typically subsides within a few days without medical intervention. Severe allergic reactions are possible but uncommon, similar to insect stings. Coexisting with dock spiders involves minimizing standing water and trimming shoreline vegetation to reduce preferred habitats near dwellings.