SynopsisCodesLook ForDiagnostic PearlsDifferential Diagnosis & PitfallsBest TestsManagement PearlsTherapyReferences

Information for Patients

View all Images (51)

Spider bite in Adult
Other Resources UpToDate PubMed

Spider bite in Adult

Contributors: Robert Norris MD, Joanne Feldman MD, MS
Other Resources UpToDate PubMed


Spiders are members of the Arachnida class, which also includes ticks, mites, and scorpions. The jaws of spiders have fangs that deliver venom via a small hole at the tips. Composition, potency, and clinical effects of venom vary among the different spider species.

Almost all species of spiders are venomous, but only a few dozen can harm humans. Of the few spiders that are of medical importance, envenomation can cause a range of clinical manifestations from skin lesions to systemic illness and, in rare cases, even death. Although tarantulas have venom, they usually cause illness from their urticating hairs. 
The severity of a spider bite depends on the type of spider, the amount of venom injected, the site of the bite, and the health and age of the patient.

Spiders of medical importance include the following:

Widow Spiders
Spiders of the Latrodectus genus are found worldwide and have neurotoxic venoms, with alpha-latrotoxin as the major component. The black widow spider, Lactrodectus mactans, is the most common widow spider in the United States and is found in woodpiles. Neurotoxic venoms cause systemic symptoms relating to cholinergic and catecholamine excess. The bite is often very painful, and systemic symptoms develop, which include hypertension, tachycardia, palpitations, diaphoresis, anxiety, shortness of breath, hyperthermia or hypothermia, excessive salivation, nausea, vomiting, and severe abdominal pain. The abdominal pain may be misdiagnosed as appendicitis or acute abdomen. The bite may have noticeable fang marks with development of a halo-like lesion around the bite. Female black widow spiders can easily be identified by the characteristic red hourglass figure present on their ventral abdomen.

Recluse Spiders
Spiders of the Loxosceles genus are found worldwide in temperate and tropical regions. Envenomation can cause local necrosis and, rarely, severe systemic symptoms due to a cytotoxic venom composed of the phospholipase enzyme, sphingomyelinase D. Cytotoxic venoms cause local tissue injury and necrosis. The bite is often initially painless. Pain, swelling, bullae, and ischemia develop minutes to hours later. Lesions may eventually ulcerate and become necrotic and gangrenous. Though systemic toxicity is rare, disseminated intravascular coagulation (DIC) may occur. The brown recluse spider, Loxosceles recluse, is regularly and erroneously blamed as the cause of necrotic lesions throughout the United States, although this spider is most commonly found in the Midwest and Southern states. It can be identified by the characteristic violin-shaped figure spanning its dorsal head and thorax.

Funnel-Web Spiders
In the Pacific Northwest, the hobo spider (Tegenaria agrestis), commonly known as the aggressive house spider, is often blamed as the cause of necrotic skin lesions. However, there is only one documented case of hobo spider envenomation causing tissue necrosis. Atrax Hadronyche species in Australia include the most dangerous spider, the Sydney funnel-web spider (Atrax robustus). The venom of this spider is neurotoxic, capable of producing severe pain at the bite site and systemic symptoms that can rarely be fatal within minutes.

Tarantulas, of the family Theraphosidae, have relatively harmless bites. However, they can disperse urticating hairs from their abdomens, resulting in local skin reactions, ocular problems, and allergic rhinitis.

Other spiders that less commonly cause significant skin irritation or dermal necrosis are as follows:

Yellow sac spiders of the Cheiracanthium genus are found in North America, Europe, Africa, Asia, Australia, and the Pacific Islands.

Wolf spiders of the Lycosa genus are common spiders found worldwide.

Banana spiders of the Phoneutria genus, of Central and South America, have extremely potent venom that is neurotoxic and can be lethal.

Six-eyed crab spiders of the Sicarius genus are found in Africa and South America and are considered to be extremely venomous but, fortunately, live in remote areas. Their venom is proteolytic.


T63.391A – Toxic effect of venom of other spider, accidental, initial encounter

403149008 – Spider bite wound

Look For

Subscription Required

Diagnostic Pearls

Subscription Required

Differential Diagnosis & Pitfalls

For more information on specific spider bites, see:

Best Tests

Subscription Required

Management Pearls

Subscription Required


Subscription Required


Subscription Required

Last Reviewed:11/15/2016
Last Updated:12/05/2021
Copyright © 2023 VisualDx®. All rights reserved.
Patient Information for Spider bite in Adult
Print E-Mail Images (51)
Contributors: Medical staff writer


Spiders are a member of the family Arachnida, and although greatly feared, spider bites are rather rare. Only a few species of spiders are able to puncture the skin to harm humans. People often mistake insect bites or skin infections for spider bites.

Who’s At Risk

The risk of being bitten by a dangerous spider is increased if you live or travel in the same area as venomous spiders and you disturb their habitat:
  • Although widow spiders are found worldwide, the black widow spider is the most common of the widow spiders throughout the United States. They are usually found outdoors in wood piles, garages, sheds, gardening pots; rarely indoors.
  • Recluse spiders are found worldwide in tropical and temperate climates, mostly in North and South America. In the US, the brown recluse spider is most common in southern and midwestern states, hiding in undisturbed quiet spots like closets, basements, cupboards, behind or under furniture, or outdoors in tree stumps or under rocks.
  • Funnel-Web spiders include the hobo spider (aggressive house spider) in the Pacific Northwest and southwestern Canada. The most dangerous, the Sydney funnel-web spider, is found in Australia.
  • Tarantulas are found worldwide, but in the US are predominant in the southwestern states. Pet tarantulas, mostly imported, have become popular throughout the United States.

Signs & Symptoms

A spider bite is typically red, inflamed, and itchy on your skin. The severity of a spider bite depends on the type of spider, your body's sensitivity to the venom, your age and health, and the amount of venom injected into your body. Spider bites have varying symptoms so it is important to identify the type of spider that bit you.

Common symptoms of widow spiders are:
  • Pain at site of bite
  • Shortness of breath
  • Rapid heart rate
  • Abdominal pain
  • Nausea
  • Vomiting
  • Salivation
Common symptoms of recluse spiders are:
  • Pain increasing during first 8 hours after bite
  • Chills
  • Fever
  • Body aches
  • Rarely, the skin can become dark blue or purple and develop into an ulcer
Common symptoms of funnel-web spiders are:
  • Pain at site of the bite
  • Redness
  • Australian species – neurotoxic effects such as trouble breathing, high blood pressure, rapid heart rate, sweating, salivating, nausea and vomiting, muscle twitches, and agitation
Common symptoms of tarantula bite:
  • Less common, red and painful bite
  • More common, itching red sting from tarantula hairs
  • Sometimes, tarantula hairs in the eye, causing eye irritation
  • Allergic reaction such as runny nose

Self-Care Guidelines

If you were bitten by a spider follow these guidelines:
  • Gently wash the bite with soap and water
  • Cool the bite with ice to reduce inflammation and pain
  • Elevate the bite if it is on a hand or arm
  • Over-the-counter medications such as acetaminophen (Tylenol) and ibuprofen (Advil) can be used as pain relievers

When to Seek Medical Care

Seek medical care if you are unsure if you were bitten by a poisonous spider. If you were bitten and have severe pain, abdominal cramps, difficulty breathing, or a growing ulcer seek medical attention immediately.

NOTE: if you were able to capture the spider, bring it with you for identification.


Your health care provider will identify the type of spider bite and treat the symptoms of the bite. Your health care provider may also give you a tetanus shot if you have not had one in the past 5 years.

For more severe reactions, and especially for children, your health care provider may place you in observation until the reactions seem to be under control.
Copyright © 2023 VisualDx®. All rights reserved.
Spider bite in Adult
A medical illustration showing key findings of Spider bite : Bite or trauma site, Erythema, Spider bite, Painful skin lesion
Clinical image of Spider bite - imageId=76956. Click to open in gallery.  caption: 'An eroded, erythematous nodule on the shin.'
An eroded, erythematous nodule on the shin.
Copyright © 2023 VisualDx®. All rights reserved.