The presence of spiders near ponds, lakes, and streams often leads to concern about whether they pose a threat to humans. The term “water spider” is commonly used to describe any arachnid found in or around aquatic environments, which creates confusion about potential danger. Understanding the actual species involved is the first step in assessing the risk of a bite and the severity of any resulting symptoms. Most spiders encountered in these habitats are non-aggressive, and their venom is primarily adapted for small prey, not for causing significant harm to people.
Identifying the Common “Water Spider” Species
The term “water spider” is ambiguous, generally referring to two groups of spiders. In North America and Europe, the spiders most often encountered are from the Dolomedes genus, commonly known as Fishing Spiders or Raft Spiders. These large, often brownish-gray spiders can have a leg span exceeding three inches, making them quite noticeable around water bodies. They hunt by running across the water’s surface tension and can even dive beneath the surface to catch aquatic insects, small fish, and tadpoles.
A distinct, much rarer species is the true Water Spider, Argyroneta aquatica, found primarily in Europe and Asia. This spider is unique because it is the only known species to spend almost its entire life underwater, breathing from a self-constructed silk “diving bell” filled with air. While both groups are associated with water, the likelihood of encountering a Dolomedes species in North America is far greater than finding the fully aquatic Argyroneta aquatica.
The Direct Answer: Do They Bite Humans?
Both Fishing Spiders (Dolomedes spp.) and the true Water Spider (Argyroneta aquatica) possess fangs and venom, meaning they are capable of biting a human. However, bites from the much more common Fishing Spiders are exceptionally rare because they are non-aggressive, shy hunters that prefer to flee at the slightest disturbance. These spiders are not interested in attacking people and will typically dart away or dive underwater when approached.
A bite would occur only as a defensive reaction, typically if the spider is accidentally trapped or squeezed against the skin, such as when one is inadvertently handling loose bark or firewood where they may be hibernating. The true Water Spider (Argyroneta aquatica) is also reported to bite defensively, especially if mishandled. The likelihood of an unprovoked bite from a water spider is minimal.
Medical Significance of the Bite
For the common Fishing Spiders (Dolomedes spp.), the venom is medically insignificant to humans. It is primarily a neurotoxin designed to paralyze small prey. A bite, if it occurs, is generally reported to feel no more severe than a bee or wasp sting. The typical symptoms are localized, consisting of temporary, mild pain, redness, and slight swelling at the bite site. These symptoms usually resolve quickly without the need for medical intervention.
For the true Water Spider (Argyroneta aquatica), the bite is widely reported to be painful, though it does not pose a serious health threat to humans. First aid for any bite should involve cleaning the area with soap and water to prevent secondary infection and applying a cold compress to manage swelling and discomfort. Medical attention is rarely required unless the individual experiences signs of an allergic reaction, such as difficulty breathing, or if the bite site shows signs of severe infection, like increasing redness, warmth, or pus formation.