Is that red, itchy bump actually a spider bite? If you didn't see the spider, it can be hard to tell. The good news is that most spiders can't do much damage to humans. The less good news is that some spider bites can cause severe symptoms — and require speedy medical attention.
"The truth is that most spiders are too small to bite us, including those adorable jumping spiders," Jody Gangloff-Kaufmann, Ph.D., an urban entomologist and coordinator with the New York State Integrated Pest Management community program at Cornell University, tells TODAY.com.
Some larger species, like wolf spiders and fishing spiders, tend to be a little more aggressive if provoked and can bite people, she says. If you're bit by one of these, the most you'll get is a lump and some itching for a few days.
The bites that experts really worry about are those from a few species of venomous spiders.
Brown recluse and black widow spiders
"The two types of venomous spiders that are really of medical concern are black widow spiders and brown recluse spiders," Gangloff-Kaufmann explains.
Black widow and brown recluse spider bites can cause more severe symptoms and, in rare cases, death, the Centers for Disease Control and Prevention say. Bites from these spiders require medical attention to treat.
Black widow spiders are found primarily in the southern and western areas of the U.S., the CDC says. They tend to live in manmade structures, Gangloff-Kaufmann says, like a shed, in the garage or underneath a bench. They're also known to live in outdoor toilets where flies gather, the CDC says.
"The one person I know who was bitten by a black widow spider was using an outhouse," Gangloff-Kaufmann says. "You just don't want to be sticking your hands into dark corners."
Black widows make irregular or asymmetric webs, Medline Plus says, and the spiders can bite people when they bump into the webs. They also typically stay within a few feet of ground level.
There are a few different "flavors" of black widow spiders, Gangloff-Kaufmann says, including brown widows, northern black widows and western black widows, all of which have a version of the classic red hourglass-shaped marking.
Meanwhile, you're more likely to find brown recluse spiders in the Midwest and southern U.S., the CDC notes. These spiders, the name suggests, can be reclusive, Gangloff-Kaufmann says. They tend to stick to secluded, dark areas, like within leaf litter or rock piles. If they go indoors, they might hide in closets, corners or shoes, the CDC says.
What do spider bites look like?
When diagnosing a spider bite, the signs to look for depend on the type of spider, Dr. Melissa Levoska, an assistant professor of dermatology at the Icahn School of Medicine at Mount Sinai, tells TODAY.com.
While both black widows and brown recluse spiders can release venom when they bite, the two types of venom actually “work quite differently,” Gangloff-Kaufmann says. Black widow venom is a neurotoxin, causing pain that can spread to a large area of the body, the CDC says. On the other hand, brown recluse venom can cause severe issues to the skin at the site of the bite.
"Brown recluse spider bites tend to be painless, but black widow spider bites can be painful," she explains. "Brown recluse spider bites can get a blister," she adds, "and they can actually develop skin necrosis, which is kind of like skin cell death."
Brown recluse bites also may develop an area of dead skin tissue called an eschar that eventually sloughs off and leaves an ulcer behind, Levoska says. But black widow bites don’t usually do that.
The early signs of a spider bite may include:
- A raised, itchy bump or rash.
- Pain at the site of the bite.
- A red or purplish area of skin around the bite.
- Sometimes, two noticeable fang puncture marks.
- Blistering at the site of the bite.
The first signs of a black widow spider bite are usually a pinprick sensation, minor swelling, redness and a target-shaped sore, Medline Plus explains. Within 15 minutes to an hour, people may start to experience dull pain in a large area of their body, depending on where they were bitten.
When it comes to brown recluse bites, people may or may not feel an immediate sharp sting, Medline Plus says. After that, pain and other symptoms tend to develop over the next few hours.
Keep in mind that your bite could also look like a wasp sting or even a rash from coming into contact with plants (like nettles) outside, Gangloff-Kaufmann says. If you're not sure what caused the bite and you start to develop worrying symptoms, it's a good idea to get checked out just in case.
Spider bite symptoms and warning signs
In addition to the bite itself, you might develop some other symptoms over the course of a few hours to days.
According to the CDC, the wider symptoms of a venomous spider bite can include:
- Muscle aches or pain.
- Headache.
- Nausea.
- Vomiting.
- Increased sweating.
- Difficulty breathing.
- Fever.
- Chills.
- Anxiety or restlessness.
- High blood pressure.
How to treat a spider bite
A spider bite on its own isn't necessarily a cause for concern.
"Most spider bites are going to be just an itchy rash, maybe some blistering and swelling at the site, and they don't even report to the doctor," Levoska says. "Most people will just manage these bites at home."
But you should seek prompt medical attention if you notice any other symptoms, particularly the above symptoms that affect the rest of your body, like widespread pain, fever or nausea, the experts say. Those are signs that you were bitten by a venomous spider, which means you'll require medical treatment.
And, certainly, if you know for sure that you were bitten by a venomous spider, you should get medical attention. Medline Plus advises people who are concerned about a spider bite to call poison control or 911 for first aid guidance and further instructions.
Treatment at the hospital for a spider bite might include antivenom, antibiotics, pain medication and wound care, depending on the type of spider responsible for the bite, MedlinePlus says. With prompt treatment, severe symptoms tend to improve within a few days while other milder symptoms may linger for weeks.
