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Spider Bites

What Are They Really and What Should You Do for Them?


Updated May 15, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Black widow spider bite

Black widow bites often have two small holes.

Image (c) David O'Connor
necrosis from possible spider bite

Necrotic arachnidism is the medical term for tissue death from spider venom.

Image submitted by shondre
brown recluse distribution map

Brown Recluse Distribution Map

(c) Rick Vetter

Most "spider bites" can't be confirmed as being caused by spiders or as being bites at all. There are only two medically significant spider species in North America: black widow and brown recluse.

Skin boils from infections are often mistaken for spider bites in the US, even by doctors. One case study of an outbreak of bites in military barracks -- at least what authorities thought were bites -- turned out to be MRSA.

Skin infections, brown recluse bites or black widows: how can you tell? It's not easy even for seasoned physicians.

Venomous (or Poisonous?) Spiders

Almost all spiders are venomous. That's how they hunt. Most spiders are too small, or their venom too weak, to be dangerous to humans. Some spiders are pretty well known and seem to get blamed for most of the spider bites out there.

In the United States, black widow spiders are often considered the most venomous. Other countries have a widow spider called the red-back spider. It's a good idea to consider any shiny black spider with a red mark to be in the widow family. Another type of widow spider, the brown widow, generally has a weaker toxin and can be found worldwide.

Brown recluse spiders have garnered plenty of attention in the last several years. Despite the large wounds often associated with brown recluse, they are much less likely to cause significant injury than black widows. Skin infections may cause boils, which are often misdiagnosed as brown recluse spider bites (see picture).

Brown Recluse spiders are only found in the Southeast United States (see map). There are several other species of recluse spider that are similar but less studied than the brown recluse. Brown recluse spiders are often described as having a violin-shaped mark on the back of their midsections, but that mark can be inconsistent.

Other parts of the world have much more dangerous species. Australia has the red back spider (similar to a black widow), white tail spiders and deadly funnel web spiders. There are more than 37,500 species of spider in the world.

Spider Bite Symptoms

Determining whether a victim has been bitten by a spider may be impossible. Studies of brown recluse spiders suggest that victims seek treatment more than three days after their bites, making it nearly impossible to identify the culprit. Black widow bites are often identified only by symptoms of its venom, without any visible local bite.

Local reactions to bites from all kinds of toxic bugs look the same:

  • redness
  • swelling
  • itching
  • pain

Victims should be concerned when a local reaction continues to get worse for more than 24 hours. Look for redness spreading away from the bite, drainage from the bite, increase in pain, numbness/tingling, or a discolaration around the bite that looks like a halo or bullseye.

Victims should also call a doctor if they are not up to date on their tetanus vaccinations.

The Spider Bite Picture Gallery (link above) contains pictures that readers submit. With each picture, you'll see that not all of the wounds were actually diagnosed by a doctor as being a spider bite. Even a doctor's stamp of approval might not be worth that much, unless the doctor is a spider bite expert. Studies suggest that emergency room doctors misdiagnose spider bites all the time, when the sore or boil is really an infection or some other type of reaction.

Anaphylaxis is always the biggest concern with any type of bug bite. If the victim exhibits any signs of allergic reaction or anaphylaxis shortly after a bug bite, call 911.

Victims should seek medical treatment if symptoms appear in parts of the body away from the location of the bite. Black widow spiders have a toxin that affects muscle contraction and nerve function. Severe brown recluse spider bites can also cause some symptoms over the entire body (systemic reaction). Look for:

  • sweating
  • chills
  • headache
  • body aches
  • stomach cramps
  • leg cramps
  • rapid pulse
  • exhaustion

In cases where the victim is feeling extremely tired or weak, call 911.

If It's Not a Spider Bite, Then What Is It?

Besides being thousands of other types of bug besides a spider, local reactions that might make you think "spider bite" can be from skin infections, chemicals, poisons, allergies or even medications.

There is no specific first aid for spider bites. Perform first aid for common bug bites if a wound is found. Systemic reactions to black widow or brown recluse bites have to be treated by medical staff, often in the emergency department.

Victims should call a doctor or go to the emergency department if symptoms persist more than 24 hours or get worse.

If you go to the doctor for a reaction, don't start out by telling him or her it's a spider bite -- even if you think that's what it is. Docs are people, too, and they are susceptible to the power of suggestion just like the rest of us. My best advice is to tell the doctor, "I have this rash (bump, boil, red spot, black spot, etc) and I was wondering if you could tell me what it is and what I can do for it."

There are many home remedies offered for the treatment of insect and spider bites. Most of these have not been shown to provide any real benefit. Meat tenderizer (papain) has even been implicated in allergies and asthma reactions to its protein. Suction syringes designed to extract toxins do not work and are a complete waste of money.


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Cacy, J, and JW Mold. "The clinical characteristics of brown recluse spider bites treated by family physicians: an OKPRN Study." J Fam Pract. Jul 1999

Isbister, GK, and J White. "Clinical consequences of spider bites: recent advances in our understanding." Toxicon. Apr 2004

Jelinek, GA. "Widow spider envenomation (latrodectism): a worldwide problem." Wilderness Environ Med. Nov 1997

Mansfield, LE, and CH Bowers. "Systemic reaction to papain in a nonoccupational setting." J Allergy Clin Immunol. Apr 1983

Mold, JW, and DM Thompson. "Management of brown recluse spider bites in primary care." J Am Board Fam Pract. Sep-Oct 2004

Muller, GJ. "Black and brown widow spider bites in South Africa. A series of 45 cases." S Afr Med J. Jun 1993

Novey, HS, et al."Papain-induced asthma--physiological and immunological features." J Allergy Clin Immunol. Feb 1979

Rees, R, et al."The diagnosis and treatment of brown recluse spider bites." Ann Emerg Med. Sep 1987

Woestman, R, R Perkin and D Van Stralen. "The black widow: is she deadly to children?" Pediatr Emerg Care. Oct 1996

Zukowski, CW. "Black widow spider bite." J Am Board Fam Pract. May-Jun 1993

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