Black Widow and Brown Recluse Spider Bite

What Are Black Widow and Brown Recluse Spiders?

  • Black widow spiders (Latrodectus mactans) may be black or brown with a leg span of approximately one to two inches. Most can be identified by a red hourglass marking on the abdomen.
  • Black widow spiders are located throughout the United States.
  • Black widow toxin causes nerve cell dysfunction and muscle cell twitching.
  • Brown recluse spiders (Loxosceles reclusa) are tan to dark brown with a leg span of approximately 1 inch. Many have a violin-shaped marking on the chest.
  • Brown recluse spiders are located mainly in the south central United States.
  • Both black widow and brown recluse spiders are common in North America and throughout the world. Human contact with these spiders is usually accidental.

Spider Bite Symptoms

Black widow a spider bites result in a halo lesion consisting of a pale circular area surrounded by a ring of redness.

Brown recluse bites are tender, red, swollen, and form blisters. The initial bite may or may not be noticed by the victim.

  • Brown recluse bites cause local swelling, pain, itching, redness, tenderness, and blisters. They eventually form large ulcers and may cause tissue necrosis (death of the tissue in the area of the bite).
  • Fever, chills, rash, nausea, and vomiting may develop.
  • More severe reactions include kidney failure, blood coagulation abnormalities, and difficulty breathing. Death can occur. Symptoms of allergic reaction may be present.

Spider Bite Treatment

If a black widow spider bite, or brown recluse spider bite is suspected, you should go to an emergency department immediately.

When to Seek Medical Care

  • Seek immediate medical care.
  • Antivenom therapy is available for black widow bites. Medications, if started early, are available to treat brown recluse bites. However, the efficacy of the medications for the treatment of brown recluse spider bites is controversial.
  • Consult a doctor about treatment with available medications.

Spider Pictures

Brown recluse spider. Note the violin pattern on cephalothorax and light-colored, hairless abdomen.
Brown recluse spider. Note the violin pattern on cephalothorax and light-colored, hairless abdomen.

Brown recluse spider head close-up.
Brown recluse spider head close-up.

Black widow spider. Note the characteristic hourglass abdominal markings
Black widow spider. Note the characteristic hourglass abdominal markings.

Black widow spider underbelly and egg
Black widow spider underbelly and egg.

Picture of the underside of a black widow spider and an egg sack
Picture of the underside of a black widow spider and an egg sack
Picture of a top view of a black widow spider
Picture of a top view of a black widow spider
Reviewed on 12/8/2017

Medically reviewed by Robert L. Cox, MD; Board Certification Internal Medicine/Infectious Disease

REFERENCE:

"Clinical manifestations and diagnosis of widow spider bites"
UpToDate.com

"Bites of recluse spiders"
UpToDate.com

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