Overview

Spider bites are usually harmless, and spiders don't usually bite unless threatened.

Spider bites can cause redness, pain and swelling, or you might not notice them at all. Many other bug bites and skin sores cause redness, pain and swelling. So unless you actually saw a spider bite you, it's difficult to be certain that your wound was caused by a spider.

Worldwide only a few species of spiders have fangs long enough to penetrate human skin and venom strong enough to hurt humans. Among these are widow spiders, with about 30 species, and recluse spiders, with more than 140 species worldwide.

Symptoms

Typically, a spider bite looks like any other bug bite — a red, inflamed, sometimes itchy or painful bump on your skin — and may even go unnoticed. Harmless spider bites usually don't produce any other symptoms.

Many skin sores look the same but have other causes, such as a bacterial infection.

Bites from some spiders, such as widow spiders and recluse spiders, might cause serious signs and symptoms.

Widow spider bites

Signs and symptoms of a widow spider bite can include:

  • Redness, pain and swelling. You might have pain and swelling around the bite, which can spread into your abdomen, back or chest.
  • Cramping. You might have severe abdominal rigidity or cramping, which is sometimes mistaken for appendicitis or a ruptured appendix.
  • Nausea, vomiting, tremors or sweating. You might experience nausea, vomiting, tremors or sweating alone or in combination.

Symptoms can last 1 to 3 days.

Recluse spider bites

Signs and symptoms of a recluse spider bite can include:

  • Increasing pain over the first eight hours after the bite
  • Fever, chills and body aches
  • A bite wound with a pale center that turns dark blue or purple with a red ring around it
  • A bite wound that grows into an open sore (ulcer) with the skin around it dying

When to see a doctor

Seek medical care immediately if:

  • You were bitten by a dangerous spider, such as a widow or recluse.
  • You're unsure whether the bite was from a dangerous spider.
  • You have severe pain, abdominal cramping or a growing wound at the bite site.
  • You're having problems breathing or swallowing.
  • The area of the sore has spreading redness or red streaks.

Causes

Severe spider bite symptoms occur as a result of the venom that the spider injects. Symptom severity depends on the type of spider, the amount of venom injected and how sensitive your body is to the venom.

Risk factors

Risk factors for spider bites include living in areas where spiders live and disturbing their natural habitat. Widow spiders and recluse spiders like warm climates and dark, dry places.

Widow spider habitat

Widow spiders can be found throughout the United States, except Alaska, and are more common in the rural South. They're also found in Europe. They are more active in the warmer months and prefer to live in:

  • Sheds
  • Garages
  • Unused pots and gardening equipment
  • Woodpiles
  • Closets and cupboards during cold weather

Recluse spider habitat

Recluse spiders are found most commonly in the southern half of the United States and in South America, where they are known as brown spiders. These spiders are so named because they like to hide away in undisturbed areas. They are most active in the warmer months. Indoors, they prefer to live:

  • In cluttered basements and attics
  • Behind bookshelves and dressers
  • In rarely used cupboards

Sometimes they get mixed up in bed linens and clothing, causing many bites to occur in the early morning.

Outside, they seek out dry, dark, quiet spots, such as under rocks or in tree stumps.

Complications

Rarely, a bite from a widow spider or recluse spider is deadly, particularly in small children.

A severe wound from a recluse spider can take weeks or months to heal and leaves large scars.

Prevention

Spiders usually bite only in defense, when being trapped between your skin and another object.

To prevent spider bites:

  • Learn what dangerous spiders look like and their preferred habitats.
  • Wear a long-sleeved shirt, hat, long pants tucked into socks, gloves and boots when handling stored boxes or firewood and when cleaning out sheds, garages, basements, attics and crawl spaces.
  • Inspect and shake out gardening gloves, boots and clothing before use.
  • Use insect repellents, such as DEET. Carefully follow directions on the package.
  • Keep insects and spiders out of the house by installing tightfitting screens on windows and doors, sealing cracks where spiders can come in, and using safe indoor insecticides.
  • Reduce debris or remove piles of rocks or lumber from the area around your home and avoid storing firewood against the walls of your home.
  • Make sure beds aren't pushed against the wall and that only the legs of the bed touch the floor. Don't store items under the bed and don't let bedding drag on the floor.
  • Remove spiders and spiderwebs from your home.
  • If a spider is on your skin, flick it off with your finger rather than crushing it against your skin.
  • When cleaning tarantula enclosures, wear gloves, a surgical mask and eye protection.

July 30, 2021
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