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What do spider bites look like?

Facts About Spider Bites

Spiders are among the most numerous and diverse creatures on earth, represented by more than 30,000 species ranging in size from less than ¼ inch to 7 inches long. The vast majority of spiders are very beneficial to man and play a major role in reducing the number of animals we consider pests. However, the occurrence of spider bites seems to attract a lot of attention and their value is quickly overshadowed by the alarm created by the thought of spider bites.

All but a relatively few species of spiders are predacious and use their venom to paralyze to defend themselves or kill their prey. Yet, there are very few species of spiders that cause serious medical problems to humans since most do not possess mouthparts that are strong enough or large enough to penetrate human skin and deliver their venom.

Spiders affect our health in various ways. One way we are affected by spiders is allergies that may result from the inhalation or other ways in which spider hairs, scales or other microscopic airborne spider parts are introduced into our bodies. Additionally, we may be affected by envenomization, the process of injecting venom by biting.

Types of Spider Bites

Many people ask how do I determine whether a spider has bitten me? Probably the best answer to that question is to examine the bite to see if there are two puncture marks that are close together where the bite occurred. If so, the bite is likely from a spider. Always seek the advice and care of a physician for the treatment of spider bites.

In the United States, spider bites that cause significant local or systemic (affecting the entire body) reactions can be categorized into three basic groups:

Bites from Widow Spiders

The Latrodectus species has venom that causes neurotoxic reactions. Development of lesions is rare with this group of spiders, but that may occur. The most important effect of their bites is the effect on the victim’s central nervous system. Symptoms will include intense localized pain, muscle cramps and pain, increased blood pressure, profuse sweating, nausea, and sometimes a skin rash. Cramping and pain in the abdominal area from a widow spider's bite can sometimes be misdiagnosed as appendicitis. Spiders in this group found in the U.S. include black, brown, and red widow spiders.

Violin Spider Bites

Loxosceles species are the spider group whose venom causes the tissue around the bite to die and form lesions (necrosis). Normally the bite symptoms are localized, but this spider group’s bites may sometimes cause systemic reactions such as anemia, blood in the urine, fever, rash, nausea, vomiting, and even coma in very rare instances. The most dangerous types of violin spiders are the various species of brown recluse spiders and hobo spiders.

Other less venomous spiders that may bite and cause less severe symptoms are the group that includes orb weaver spiders, funnel-web spiders, wolf spiders, jumping spiders, tarantulas, and crab spiders. While pain may accompany their bites, it is moderate to slight, temporary, and only rarely produces serious reactions.

Are all spider bites dangerous?

All spiders with the exception of those in the family Uloboridae use their venom to paralyze or kill prey they must consume in order to survive. Uloboridae is a very small group of spider species found primarily in our Southern states. These spiders have chelicerae (fangs), but no venom gland. All other spiders found in the United States have venom glands and fangs, but their fangs may be too short to penetrate human skin and/or their venom may not be potent enough to cause a harmful reaction. Therefore, these spiders can bite, but are not considered harmful, other than producing minor, short-lived symptoms resulting from their bite.

Spider publications generally report that only about 50 species of spiders are implicated in bites that are likely to cause medical implications beyond temporary localized pain and slight swelling at the site of the bite. The exception to this generality is the bite from the widow and recluse spiders.

Many spiders have fangs that are not capable of breaking the skin, while other species possess venom that causes little or no reaction. Spiders are usually very timid and will only bite in self-defense if mishandled, cornered, or injured. Even when they bite, spiders do not always inject venom. The severity of the reaction to a spider bite will differ among individuals depending upon the amount of venom injected and the autoimmune responses of the person bitten. But in general, most spider bites are less painful than a bee sting and involve only localized pain, redness and swelling. Also, field and laboratory investigations have shown the majority of suspected or misdiagnosed "spider bites" are caused by other arthropods such as insects and ticks, or skin irritations.

Most Common Spiders That Bite in the US

While it is possible for almost any spider to either bite or attempt to bite someone who has disturbed, provoked or is handling them, the following medically important spiders and others considered to be of relatively minor importance are perhaps likely to bite humans.

Widow Spiders

Four species of widow spiders are found in the United States - the southern black widow, the northern black widow, the red widow and the brown widow. While their venom causes serious, medically important symptoms, these spiders are not considered to be aggressive biters.

Recluse Spiders

The U.S. is home to 11 species of recluse spiders. The most common of which is Loxosceles reclusa, which can be found in the north between Nebraska and Ohio and all the way south between Texas and Georgia.

Other species of recluse spiders include the desert recluse, L. deserta found mostly in the Sonoran and Mojave deserts and the San Joaquin Valley foothills, plus other species identified as L. arizonica, L. apachea, L. blanda, L. devia, L. russelli, L. palma, L. rufescens, L. laeta, and L. martha. All species of Loxosceles spiders have venom capable of causing necrotic skin lesions; however, like the widow spiders, they are also considered non-aggressive biters.

Hobo Spiders

Hobo spiders have been reported to have a bite that can cause tissue necrosis similar to a brown recluse bite. However, the hobo spider's bite isn't persuasively identified as the cause of necrosis.

Yellow Sac Spiders

Yellow sac spiders are a type of nighttime hunting spiders that search for prey rather than catching their prey within a web. Therefore, these spiders may come into contact with people while they are gardening or working in a preferred yellow sac spider habitat. Yellow sac spiders can deliver painful bites. However, they rarely result in serious medical issues.

Parson Spider

The parson spider, like nearly all other spiders, is not regarded as medically important. However, their bite is painful, and some individuals may experience an allergic reaction with variable symptoms.

Wolf Spiders

Wolf spider bites are not medically important and feel much like a bee sting.

Common House Spiders

The common house spider is especially prevalent in houses, but their bite is not medically important.

Tarantulas

Tarantulas that are native to the U.S. are not likely to bite unless handled or otherwise provoked. Their bites may cause localized pain and redness but no serious medical problems. Of note is the presence of hairs on the tarantula's body that can cause irritation symptoms of human skin.