Fishing spiders, belonging to the genus Dolomedes, are some of the largest spiders found throughout North America. Due to their intimidating appearance, many people ask if they are poisonous or venomous. They are venomous, but they are not considered dangerous to the average healthy human.
Understanding the Threat Level
The distinction between “poisonous” and “venomous” is crucial for understanding the threat a spider poses. A creature is considered poisonous if its toxins are harmful when absorbed, inhaled, or ingested, like certain mushrooms or frogs. Spiders, including the fishing spider, are venomous because they produce a toxin that must be actively injected into a victim using specialized fangs.
The venom contains a complex mix of neurotoxins, which are highly effective against the small aquatic insects and fish they hunt. However, this venom is not considered medically significant to humans, meaning it rarely causes serious health issues. They are naturally shy and will typically flee or play dead rather than attack a person. Furthermore, their fangs are often too small or weak to successfully penetrate human skin unless the spider is severely provoked or accidentally pressed against the skin.
Identifying Fishing Spiders
Fishing spiders are easily identified by their large size, with some species reaching a leg span up to 3.5 inches. Their coloration typically ranges from brownish-gray to dark brown, often featuring black and light brown markings and distinctly banded legs. This combination of size and color often leads them to be mistaken for large wolf spiders or even tarantulas.
Common names for these spiders include dock spiders, raft spiders, and nursery web spiders, all of which reflect their lifestyle. They are expert hunters known for their unique ability to walk or glide across the surface of water. They can also dive beneath the water, using bristly hairs on their body to trap air, allowing them to remain submerged for extended periods to ambush prey.
Species like the Dark Fishing Spider (Dolomedes tenebrosus) are frequently found far from water in wooded settings and occasionally enter homes through basements or crawl spaces. They often use man-made structures like boat houses, docks, and damp storage areas as refuge.
Bite Symptoms and Treatment
If a fishing spider bite successfully occurs, it is usually a defensive action, and the reaction is typically localized and mild. The initial sensation is often described as an immediate, sharp prick or pain, similar in intensity to a bee or wasp sting. This is generally followed by localized symptoms such as mild swelling, redness, and some itchiness at the bite site.
Systemic reactions, which affect the entire body, are exceedingly rare and usually only occur in individuals with specific sensitivities or allergies to spider venom. For standard, mild bites, first aid involves washing the area thoroughly with soap and water to prevent secondary infection. Applying a cold compress or ice pack can help reduce any swelling and discomfort. Over-the-counter pain relievers or antihistamines may be used to manage pain and localized swelling.
A person should seek professional medical attention if symptoms worsen, if the pain persists beyond 24 hours, or if signs of an allergic reaction appear. These signs include spreading redness, fever, chills, nausea, or difficulty breathing.