Spider Bite

A spider bite is an injury resulting from the bites of spiders or other closely related arachnids.

Spiders are active hunters and rely heavily on their bites to paralyze and kill their prey before consuming it. They also bite in self-defense. While many spiders will never attack animals larger than themselves, some—e.g., Atrax robustus—exhibit a rather aggressive behavior and will stand their ground when approached by larger animals. Most spider bites, however, occur when humans unintentionally press up against spiders and receive a defensive bite. On rare occasions, spiders may make prey mistakes and bite a human finger or other body part as though it were a caterpillar or other such insect.

Only spiders of fairly large species possess chelicera long enough to penetrate human skin, and most of those are females. The effect of a bite on humans is dependent on both the toxicity of the venom and the amount of venom. About 98% of the bites inflicted by species that are large enough that their bites are noticed will have no serious medical consequences. Of those bites that humans notice, venoms can include necrotic agents, neurotoxins, and agents such as serotonin. Only some two hundred species in twenty genera (out of over 40,000 known species) are known to have serious, potentially lethal bites.

In most cases of bites, the chief concern is the spider's venom, although in some cases medically non-significant spiders can transmit infectious diseases. Spiders regarded as dangerous possess venom that is sufficiently toxic to humans that a single bite can deliver a medically significant dose. Only two spider families are known to be non-venomous, i.e. lacking venom glands. They are Uloboridae, Holarchaeidae. In addition, their fangs can often inflict infections spread through the skin, mostly due to their large size, which in theory could represent more danger than the bite of a non-lethal venomous spider species.

Spider bites may be misdiagnosed by both the general public and medical practitioners. Many other conditions both infectious and non-infectious can be confused with spider bites. Many of these conditions are far more common and more likely to be the source of necrotic wounds.