How to treat spider bites and when you need to see your doctor

It's not uncommon to be squeamish about spiders, but it is uncommon to be bitten by one. While several species in the United States can bite, only two types — the black widow and the brown recluse — inject venom that can be dangerous to humans.

Spider bites: What you need to know

Spiders are arachnids, not insects. Unlike mosquitoes, ticks, and fleas, they are not out for blood; instead, they bite people as a defense mechanism if disturbed. A spider might bite, for example, if you accidentally touch it, try to trap it, or intentionally provoke it.

Most spiders' jaws are small enough that even if they try to bite, their fangs can't penetrate the skin. Those that can pierce the skin include yellow sac spiders, hobo spiders, and wolf spiders. While bites from these species may hurt (similar to a bee sting) and cause redness and itching around the area, they are unlikely to cause complications.

Black widow and brown recluse spiders, however, produce venom that can cause a serious reaction in humans — including, rarely, death.

Black widow spiders are about an inch long, with shiny black bodies and a red hourglass shape on the underside of the abdomen. Only female black widows pose a risk to humans.

The brown recluse spider is about half an inch long and light tan to dark brown in color, with long skinny legs and a distinctive violin-shaped pattern on the back of its upper body. Both sexes of the brown recluse are venomous.

This website can help to identify the type of spider you've encountered.

How to tell if you've been bitten by a spider

The only sure way to know if you've been bitten by a spider is to catch it in the act of biting you. Spider bites from many types of spiders can cause itching, redness, stiffness, swelling, and pain. Or they may cause no symptoms at all.

Signs and symptoms of a black widow spider bite

Signs and symptoms of a black widow spider bite include:

• two pinprick-sized fang bites, close together
• sharp pain during the bite
• swelling, redness, numbness, and soreness
• severe muscle pain and cramping
• rapid heartbeat, high blood pressure, and difficulty breathing (in some cases)
• headache
• increased saliva and sweating
• light sensitivity
• muscle weakness
• nausea and vomiting
• facial swelling.

It's rare, but black widow spider bites can cause death. Young children, people who are ill, and older adults are at the greatest risk.

Signs and symptoms of a brown recluse spider bite

Signs and symptoms of a brown recluse spider bite include:

• a stinging sensation followed by intense pain
• itching
• reddish or purplish circle around bite
• chills and a general feeling of discomfort
• a small pus- or blood-filled blister with increased redness and swelling
• restlessness
• fever
• sweating
• nausea
• tissue damage around the bite that can become severe if not treated promptly.

Rarely, a brown recluse spider bite may lead to:

• coma
• blood in urine
• yellowing of the skin and whites of the eyes (jaundice)
• kidney failure
• seizures.

Death from brown recluse spider bites is more common in children than adults.

Treating spider bites

Most spider bites can be treated at home with the following first-aid measures:

• Wash the area with warm, soapy water.
• Apply an antibiotic cream on the bite to help prevent it from getting infected.
• Put a cool washcloth or an ice pack on the bite to reduce swelling.
• Take an antihistamine to relieve swelling and itching.
• Take ibuprofen or acetaminophen if pain in the bite area persists.

When to see a doctor

If you think you've been bitten by a brown recluse or a black widow spider, alert your doctor right away.

You may receive antivenom (a medicine to counteract the venom, also called antivenin) if you were bitten by a black widow spider. There is no antivenom for brown recluse spider bites. In addition, for both types of spider bites, you may receive breathing support, intravenous (IV) fluids, or medications to manage other symptoms, as needed.

Seek immediate emergency treatment if you have trouble breathing, an elevated heart rate, or facial swelling. These can be signs of a severe allergic reaction (anaphylaxis).

Preventing spider bites

The best way to avoid being bitten by a black widow or a brown recluse spider is to know what they look like and where they hang out. Brown recluse spiders can be found in the Midwest and Southern regions of the U.S., up to Illinois. Black widow spiders are found throughout the U.S. Both types prefer dark, moist, quiet areas, like wood, brush, or rock piles, or storage spaces like garages, sheds, or attics.

Wear work gloves, long pants, and shirts with long sleeves when handling stacks of wood or brush. Brush off (don't crush) any spiders that get on you. Reduce clutter in garages, basements, and attics. To keep spiders from getting into the house, seal up cracks and spaces where spiders can get in.