Spider Bite (?)
If I had a dollar for every time a patient told me that they were bit by a spider, I could retire (or at least buy a condo in San Diego).
Poisonous spider bites are extraordinarily rare; wounds blamed on spiders are extraordinarily common. I have seen dozens of patients who thought they had been bitten by a spider, and I have never made a diagnosis of an actual spider bite. That is until now.
It started off as a phone call from a primary care physician. He described a man that he felt had a spider bite on his hand. I was a little disappointed at first; usually the primary care docs are pretty good at dispelling the blame-it-on-a-spider myth, but this guy was convinced.
“Well, I don’t know,” I said, “send him over and I’ll take a look.” In dermatology, the skin always tells the best story.
When my patient arrived I took one look and thought: Wait a minute, this might be the real thing. It didn’t look like a typical staph or MRSA infection (which is almost always the true diagnosis).
The patient had been cleaning his garage in a rural, desert part of the county and had pulled a gas stove out of his attic. He thought nothing of it until several hours later when his finger began to throb. The next day he had pain and swelling of the middle finger on his right hand. This progressed to redness and tenderness spreading up his hand and arm. When I saw him, it was 3 days later, and the redness had subsided, but he had this purple-red wound on the back of his finger.
Now in truth, I cannot definitively diagnose him with a spider bite unless he either saw a spider bite him or knew for a fact that his garage was infested with spiders. Poisonous spiders are rare in southern California and spiders that cause local necrosis even more rare.
Despite the widespread belief that skin wounds are caused by bites from various, ferocious spiders, only a handful of spiders can give necrotic (deep, dead skin) wounds. The most likely culprit of such wounds, the brown recluse spider, Loxsoceles reclusa, does not live in southern California.
There is another plausible explanation; there is a close cousin of the brown recluse called Loxsoceles deserta that does live in the desert regions of southern California. It is possible he was bitten by one of those spiders.
If you think you have been bitten by a spider, remember these facts:
- Spider bites are exceedingly rare. Studies have shown that the number of spider bites attributed to spiders far exceeds the number of poisonous spiders living in that area. For example, in South Carolina, there were 478 diagnoses of brown recluse spider bites one year, but entomologists were only able to confirm brown recluse spider in the whole state (it must have been the “Jaws” of spiders).
- If you did not see a spider bite you, then it is very unlikely that you were bit by a spider.
- Spiders do not come out at night to bite you. They are, in fact, reluctant to bite, even when provoked.
- Very few spiders in the US (some would say only one spider, the brown recluse) are likely to cause a necrotic wound.
- The black widow spider is also a poisonous spider, but it releases a neurotoxin that causes abdominal pain and paralysis. It does not cause a necrotic skin wound.
Brown recluse spider with characteristic violin clearly visible on its back.
My final diagnosis: Spider bite. I think.
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I had a brown recluse bite to the dorsum of my right hand about 10 yrs ago. Started as a red, painful spot and progressed to a necrotic area within 12 hours with lymphangitis up pass the elbow. I was tx’d with antibiotics, steroids, and hyperbaric O2. It was amazing to see the improvement with the hyperbaric tx!!! I can still find the scar, but no one else can.
I frequently get referrals for “spider-bite” which turn out to be simple soft tissue abscesses. People can be very fixated on blaming the spiders. I’ve tried to explain that there can’t be THAT many spiders biting people in the community, as we are not in the movie Arachnophobia. Sadly, most of my patients clearly have no idea what movie I am referring to, and then I feel old.
We had an ant bite my daughter once. Observed. A red spot appeared, so I advised her to stop itching it. But over the next two days it grew to about the size of a credit card and was warm to the touch.
We took her in with a “What the heck, it was just an ant bite.” Diagnosed a staff infection, gave her antibiotics with a double dose the first 24 hours and a strong “watch what happens in the next couple of days”.
I wonder if we would have thought it was a spider bite if we hadn’t seen the ant?
It just goes to show that spiders have a strong presence in our cultural lexicon of story.
I spent a month with Dr. Bernie Ackerman, renowned dermatopathologist and controversial figure. As we looked at skin samples under the microscope I used to get a laugh when he “ruled out arthropod assault” as the cause of the lesion. The idea of being assaulted by a spider struck me as quite whimsical. But I was the only one laughing.
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My freind has been bitten by a spider she has three lumps at the top of her leg what shall we do??? Please help !!!
Megan-
Your friend should see a physician.
Remember, this blog is for educational purposes only. I do not provide medical advice on this site nor should you interpert any information provided here as medical advice or use it as a substitute for seeing a physician.
I hope your friend is well soon.
J Benabio, MD
Wondering if anyone could help me diganose a spider bite. I was bit two days ago on the back of my arm. At first the spots were red and hard. day two large blisters have form and one has popped. I’ve looked on the net and it sounds like a brown recluse bite. Any help would be appeciated. thanks
While in St. John, USVI, I got a bite on my forehead that started as a small bump and swelled. By day 3, it swelled half of my forehead with another small mark on the bridge of my nose. By day four, I had pain on top of my head and in my right ear. By day 6, three tiny dots appeared and by day 7, a necrotic area in the shape of an L was on my forehead. I’ve been treated by antibiotics and now Dr. #4 feels it is shingles, not a bite. I don’t have the symtoms of shingles! Any ideas? -Barb
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