Patient education: Spider bites (The Basics)

How common are spider bites? — Spider bites are very rare. Most spiders' fangs are not strong enough to poke through human skin. Also, spiders do not usually bite unless they are crushed between you and another object.

Most people who think that a spider bit them were usually bitten by a different insect, such as a tick. Also, some skin infections can look like a spider bite.

How dangerous are spider bites? — Most spider bites are harmless. The poison that most spiders inject when they bite (called "venom") is not toxic to people. But a few types of spiders can give painful bites. In rare cases, the bites get infected or cause other serious symptoms (picture 1).

Some types of dangerous spiders live only in Australia or South America. But some are found in countries all over the world, including the US (table 1).

What are the symptoms of a spider bite? — Symptoms include a small, raised bump on the skin. On lighter skin, the bump might look red. On darker skin, the bump might look reddish-brown. The bite might itch or burn.

Some bites do not start to hurt until a few hours after the bite. The pain can range from a slight prickly feeling to very bad pain.

In rare cases, spider bites can cause:

●Increasing swelling and draining pus

●Flu-like symptoms such as feeling tired, nausea, vomiting, and fever

●Sweating

●Very bad muscle pain

●Very bad belly pain

●Dead tissue – When this happens, the center of the bump turns darker red, blue, or black, then dries out and forms a sore. This is called "necrosis" and can happen several days after a spider bite. The sore is usually about the size of a quarter but can grow larger. Most heal after a few weeks, but some last for months.

What should I do if a spider bites me? — If you are bitten by a spider, you should:

●Wash the area with soap and water.

●Put a cold gel pack, bag of ice, or bag of frozen vegetables on the painful area every 1 to 2 hours, for 15 minutes each time. Put a thin towel between the ice (or other cold object) and your skin.

●If you can, keep the bitten area raised up above the level of your heart.

●Try to figure out what type of spider bit you.

Should I see a doctor or a nurse? — See a doctor or nurse if you get any of the rare symptoms listed above.

How are spider bites treated? — Treatment involves cleaning the area well and taking medicines if needed. Depending on your symptoms, your doctor or nurse might recommend:

●Medicine for pain, such as ibuprofen (sample brand names: Advil, Motrin)

●Medicines to treat muscle spasms, called benzodiazepines

●A tetanus shot – Tetanus is a serious infection that causes muscle spasms and stiffness. It is caused by bacteria that can get into your body through a cut, scrape, or bite.

●Antibiotics – If there are signs of infection (such as a fever, spreading redness, or pus coming from the bite), a doctor will prescribe you antibiotics. But most spider bites do not get infected.

People who have dead tissue because of a bite sometimes need surgery to remove the dead tissue.

People who are bitten by a widow spider and have severe pain and muscle spasms that don't get better with other treatments sometimes get a special medicine called "antivenom."

What can I do to reduce the chances of getting a spider bite? — To avoid a spider bite, be extra careful in places where dangerous spiders live (table 1).

More on this topic

Patient education: Insect bites and stings (The Basics)

Patient education: Bee and insect stings (Beyond the Basics)
Patient education: Imported fire ants (Beyond the Basics)