The Dark Fishing Spider, Dolomedes tenebrosus, is a large and common North American arachnid often encountered near water sources or in damp, secluded areas. Its impressive size frequently leads people to question its potential threat level. While it possesses fangs capable of biting, such incidents are extremely rare, and the resulting bite is not medically significant for most people. This species is non-aggressive and poses minimal risk.
Identifying the Dark Fishing Spider
The Dark Fishing Spider is one of the largest spiders found in North America, with a substantial body and leg span. A mature female’s body length can reach about one inch, but her long, sprawling legs can give the spider an overall diameter exceeding three inches. This size often leads to misidentification as a tarantula or a large wolf spider.
The coloration is typically a mottled mix of light brown, gray, and black, providing effective camouflage against bark and stone. A distinguishing feature is the series of black, W-shaped markings that run down the dorsal surface of the abdomen. The legs are notably long, often held out in a wide stance, and are ringed with dark bands and covered in long, prominent spines. Although they are frequently called “fishing spiders,” this particular species is often found far from water in dry wooded areas, under logs, or inside dark, humid structures like basements and sheds.
When and Why Bites Occur
Dark Fishing Spiders are wandering hunters that stalk small insects, fish, and tadpoles using venom, rather than building webs. Their primary instinct when encountering a human is to flee. They are naturally shy and will typically dart away at the slightest movement or disturbance in their vicinity.
Bites on humans are strictly defensive, triggered only by a perceived threat that prevents the spider from escaping. This usually happens when the spider is accidentally trapped against the skin, such as when a person attempts to handle it, or if it is inadvertently pinned down inside clothing or bedding. Since they are non-aggressive, the chances of being bitten are low.
Effects of the Venom and Necessary Care
The venom of Dolomedes tenebrosus is not considered a serious medical threat to humans. If a defensive bite does occur, the symptoms are generally mild and localized, often compared to the discomfort of a bee or wasp sting. Immediate effects typically involve minor, burning pain at the site of the bite, followed by slight redness and localized swelling.
While these symptoms can be uncomfortable, they usually subside on their own within a few hours. The bite is not associated with the severe systemic effects of more dangerous species. The first step is to clean the bite area with soap and water to prevent secondary bacterial infection. Applying a cold compress can help reduce swelling and alleviate pain. Seek medical attention if symptoms worsen, or if signs of an allergic reaction, such as difficulty breathing or widespread swelling, begin to appear.