A black widow spider, with its tell-tale red hourglass. If you feel pain when the spider bites, this is likely the culprit.

by James Hubbard, MD, MPH

I’ve seen a lot of spider bites in my day, and more often than not, the spider is never seen. Over the years I’ve developed several tricks for how to identify the spider by the bite.

There are three types of poisonous spiders in the U.S. The brown recluse is found in the southern two-thirds of the country. It likes to hide in boxes so I often wonder if it doesn’t catch an occasional ride by freight. The hobo spider likes it out west. The black widow has been found in every state but Alaska.

Here are my tips on how to identify a spider bite.

1. Evaluate the Pain

If you feel pain when the spider bites, it’s likely a black widow, whose bite is often but not always painful. You may also develop severe body aches and fever.

A brown recluse spider bite is a slight sting at best. Most of the time you feel nothing. They hide in or under boxes, under your bed sheets, in your clothes. The first you know about it is the pain that develops several minutes to hours after the bite.

A brown recluse spider bite, two months later. This is the eschar—the black, leathery, dead tissue—that can form over the wound. The photographer writes that it was surgically removed about a month after this photo.

A hobo spider’s bite feels similar to a brown recluse’s, and the pain also occurs minutes to hours after the bite.

2. Look at the Skin Damage

That’s the key to the brown recluse spider bite. You may not know when it bit you, but the bite area becomes red, blistered, or black. The area starts out small, and the redness spreads. A black spot of dead tissue develops in the middle of the redness. This dead tissue can be anything from small and superficial to deep and large—sometimes enough to warrant a skin graft when everything’s said and done. As the tissue dies, the area becomes very painful.

The hobo spider can cause skin damage, but less so than the brown recluse.

The black widow spider bite causes a red spot that’s sometimes hard to see. (More obvious: It can cause plenty of muscle aches and cramping throughout the body for one to three weeks.)

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How to Treat a Bite From a Poisonous Spider

If you can get to a doctor, do so. If you can’t, consider the following.

If you think the spider was a brown recluse or hobo:
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  1. Slow the venom’s spread: Apply ice, and keep the area at heart level or above.
  2. Prevent infection. As the black layer of dead skin (eschar) sloughs off, treat the wound as you would any other, by keeping it clean and covered and applying antibiotic ointment or honey. Some large wounds take several weeks to heal. If it starts looking infected, you’ll need oral antibiotics.
  3. Treat the pain. Take an over-the-counter pain reliever.

Some think steroids might decrease the extent of skin damage from a brown recluse bite. Sometimes skin grafts are required when the wounds are too big to heal on their own.

If you think the spider was a black widow take a pain reliever like ibuprofen or acetaminophen for the muscle cramps.

Within minutes to hours, a black widow bite can lead to severe chest and abdominal pain mimicking appendicitis or a heart attack. It can make your blood pressure go up, which may need to be treated. (Possible signs include an increased heart rate and a flushed face.) If you can’t get to a doctor, rest to try to lower the blood pressure. In worst cases, antivenin may be given.

The good news is it’s very rare to die from a spider bite.

Has anyone ever had a brown recluse, hobo, or black widow bite? How did you identify the spider type? What were the symptoms? How was it treated? How are you doing now?

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Black widow photo by Texas AgriLife Extension Service. Photo of brown recluse spider bite by Jeffrey Rowland.