What are spider bites?

All spiders in the U.S. have poison (venom). But the fangs of most spiders are too short or too fragile to break through human skin. Or their venom is too weak to cause damage to people or pets. Most spider bites cause only minor, local reactions at the bite site. But some spider bites can be deadly.

What causes dangerous spider bites?

Most spiders found in the U.S. are harmless, except for the brown recluse and the black widow spiders. Both of these spiders are found in warm climates:

• Brown recluse spider. The brown recluse spider (violin spider) is about 1 inch long and has a violin-shaped mark on its head. It is often found in warm, dry climates. And it likes to stay in undisturbed areas, such as basements, closets, and attics. It is not an aggressive spider. But it will attack if trapped or held against the skin. No deaths have been proven in the U.S. from a brown recluse bite. But a small number of bites have been reported.

• Black widow spider. A black widow spider is a small, shiny, black, button-shaped spider. It has a red hourglass mark on its belly. And it prefers warm climates. Black widow spider bites release a poison (toxin) that can damage the nervous system. These bites need emergency medical care.

What are the symptoms of dangerous spider bites?

The symptoms vary based on the type of spider.

Brown recluse spider bites. Venom from the brown recluse spider often causes local skin tissue damage. Symptoms of these bites include:

• Burning, pain, itching, or redness at the site. (This is often delayed and may occur a few hours or days after the bite.)

• A deep blue or purple area around the bite, surrounded by a whitish ring and large red outer ring similar to a target or bulls-eye

• An open sore (ulcer) or blister that turns black

• Headache, body aches

• Rash

• Fever

• Nausea or vomiting

Black widow spider bite. Venom from the black widow spider has a toxin that can damage your nervous system. Symptoms of these bites include:

• Immediate pain, burning, swelling, and redness at the site (double fang marks may be seen)

• Cramping pain and muscle stiffness in the stomach, chest, shoulders, and back

• Headache

• Trouble breathing

• Dizziness

• Rash and itching

• Restlessness and anxiety

• Sweating

• Eyelid swelling

• Nausea or vomiting

• Salivation, tearing of the eyes

• Weakness, tremors, or paralysis, especially in the legs

Many of the symptoms of a brown recluse spider bite and a black widow spider bite may be caused by other health problems. Always see your healthcare provider for a diagnosis.

How are dangerous spider bites diagnosed?

A spider bite is diagnosed based on your history and your symptoms. A definite diagnosis of a spider bite needs all of these:

• You saw the spider bite your skin.

• The spider was captured and correctly identified by someone who is an expert on insects (entomologist).

• There is a skin sore lesion or you have overall (systemic) physical symptoms related to the spider bite.

• Any other conditions that could also cause the physical symptoms have been ruled out.

In most cases, a spider bite is not the cause of the symptoms. Such things as infections, bites and stings of other insects, and common skin conditions and infections can cause the symptoms. Brown recluse spider bites are often diagnosed by mistake. They are often diagnosed in areas that don’t have recluse spiders.

How are dangerous spider bites treated?

The treatment may include:

• Washing the area well with soap and water.

• Applying a cold or ice pack wrapped in a cloth to the site. Or apply a cold, wet washcloth (compress) to the site. To make an ice pack, put ice cubes in a plastic bag that seals at the top. Wrap the bag in a clean, thin towel or cloth. Don’t put ice or an ice pack directly on the skin.

• Protecting against infection, particularly in children, by applying an antibiotic lotion or cream.

• Taking medicine for pain.

• Raising (elevating) the site if the bite happened on an arm or leg. This can help prevent swelling.

For a brown recluse spider bite, you may need emergency care for more treatment. Depending on the severity of the bite, surgical treatment of the area may be needed to correct skin damage. Hospitalization may be needed.

For a black widow spider bite, you may need emergency care right away for more treatment. Depending on the severity of the bite, treatment may include muscle relaxants, pain relievers and other medicines, and supportive care. In rare cases, a medicine called antivenin may be needed. But it is often not needed. Hospitalization may be needed.

Quick treatment of both types of spider bites is key to preventing more serious complications, especially in children.

What are possible complications of dangerous spider bites?

Tetanus spores can infect spider bites. Keep tetanus boosters up-to-date (every 10 years).

Can dangerous spider bites be prevented?

Possible exposure to dangerous spider bites can be decreased by:

• Inspecting or shaking out any clothing, shoes, towels, or equipment before use.

• Wearing a long-sleeved shirt and long pants, hat, gloves, and boots when handling stacked or undisturbed piles of materials.

• Decreasing empty areas between piled or stored materials.

• Removing debris and rubble from around the outdoor recreational or work areas.

• Trimming or removing tall grasses from around outdoor recreational or work areas.

• Storing clothing and outdoor equipment in tightly closed plastic bags.

Key points about spider bites

• Most spiders found in the U.S. are harmless, except for the recluse and the widow spiders.

• Venom from the brown recluse spider often causes local skin tissue damage.

• Black widow spider bites release a poison that can damage the nervous system. Emergency care is needed right away.

• Symptoms of a brown recluse spider bite include a deep blue or purple area around the bite, surrounded by a whitish ring and large red outer ring like a target or bulls-eye.

• Symptoms of a black widow spider bite include cramping pain and muscle stiffness. There may also be weakness, tremors, or paralysis, especially in the legs.

• Prompt treatment of both types of spider bites is key to preventing more serious complications, especially in children.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

• Know the reason for your visit and what you want to happen.

• Before your visit, write down questions you want answered.

• Bring someone with you to help you ask questions and remember what your provider tells you.

• At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.

• Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.

• Ask if your condition can be treated in other ways.

• Know why a test or procedure is recommended and what the results could mean.

• Know what to expect if you do not take the medicine or have the test or procedure.

• If you have a follow-up appointment, write down the date, time, and purpose for that visit.

• Know how you can contact your provider if you have questions, especially after office hours or on weekends.