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.

You might also like:

How to get into Dermatology

Toasted Skin Syndrome

Eeeewh! Bedbugs

Like this blog? Grab The Derm Feed

21 thoughts on “Spider Bite (?)”

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. My freind has been bitten by a spider she has three lumps at the top of her leg what shall we do??? Please help !!!

  6. 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

  7. 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

  8. 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

  9. Pingback: SpiderBites.Me
  10. kerry quick says:

    On Dec 24th 2008 I noticed a huge blacked rise under my arm pit the pain is undescribable the redness stretches the size of your index finger long and the pain goes from wrist to down my side did i mention the pain is undescribable it looked like a volcane and has erupted and is very very green and puss pours from it within 6-8 hours I couldn’t hardly move had no energy and found it hard to breath as of today 12/29/08 the green part it falling out and I can see a huge hole under neath my husband has been bitten on his forearm in a hotel room and on the back of his foot about 3 months ago it was bad I believe I got bitten one of 3 ways I went iut to the shed to retrieve x-mas presents to wrap theres ton’s of spiders out there mostly in boxes and cabinet’s or in one of 2 sweatshirts i put on that had been stored by the back door same way I was bitten in oct of 07 beside belly button not painful skin had same symptoms though when i showed my in-laws the bite I have now they gasped and said that’s a fiddleback bite I live in tennessee and it’s nothing to see fiddlebacks and black widows all the time I may have rolled over on it in my sleep I sleep with my right arm up against wall exposing that area who knows but I have personally killed about ten of them in my kitchen floor in the past year. I cannot describe in words the pain I’m in I don’t believe child birth is as painful as this no joking. tell me what you think I can text you a picture if youd like just let me know. thanks for you time

  11. you are totally wrong that spiders dont bit you at night. several species are parasites that hide near your bed and feed on you frequently.
    they eat off the top layer of skin and then when the blood oozes a bit the feed on that too. they MAY secrete some kind of anesthetic to keep you from feeling it and waking you. they dont eat much but some of the breeds do cause allergic kindof immune reactions like arthritis kind of stiffness in the morning. they have a pattern of eating and making a small wound – then when they get deep enought or long enough in one spot to rouse you a bit they move a few mm and start over, the line of dits gets smaller and smaller – up to 7 or 9 little wounds – sometimes only one or a few dots. so stop saying they dont parasite off people at night – they absolutely do – more than one breed does it.

  12. Question on muscle pain after a spider bite?? I got bitten by a spider in Nevada in late March which resulted in a large blister and then necrosis of the skin in that area followed by cellulitis. The doctor prescribed antibiotics to clear up the infection which took about 6 weeks for the wound to stop oozing. The bite was on my left abdomen. Within a month of the bite, I started to have pain in my left hip area. It feels as if the muscles just can’t support my hip and lower back. The pain is so intense it will wake me from a deep sleep and bring me to tears when I try to change sleeping positions. The dr has taken a hip xray and says it’s moderate arthritis. Has anyone else experienced muscle pain/atrophy following a spider bite? I’ve not injured my hip in any way and the anti inflamatories the dr prescribed only minimally mask the pain. I’ve not ever had any pain due to arthritis in the past.

  13. Paul, thanks so much for saying this — I have been looking all over the internet to identify a few insect bites that my son received one night last week. He got four bites in widely separated areas (back, forearm, chest) and each bite has two to three puncture wounds in a very straight row, very close together (about 1/16″ between each puncture). Every website I see all I read is three holes in a row mean bed bugs, but these three punctures are clearly NOT three bites — they are one bite, with three punctures. Two punctures would mean a spider. I cannot find anything that identifies three punctures. But at last I found someone (thanks Paul) who will at least say there are creatures that do come out at night and bite like this!

  14. 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.

  15. Thanks for your picture. I was bit by something on my ARM. Several days later I had the same type of place come up on my middle finger. My docs had no idea what was going on. Thanks

  16. Well I don’t like spiders there iky so yupppp

  17. Carol Andrews says:

    Believe it or not, a Daddy Longlegs bit me on the left foot between my big and second toes. This is practically unheard of. It may have happened because he had been threatened when I flipped him/her off my sleeve and itlanded on my foot. At first there was a burning sensation as it turned red. Then it spread turning dark blue and red and my toes and the area above my toes became swollen. I couldn’t put a shoe on for a week. Large red areas appeared on my arms,legs, torso and the left side of my face below my eye became swollen and red. I was put on Arythromycin, kept my foot elevated with ice bags. I believe that the spider was able to pierce the
    thin skin between my toes. (Incidentally, I live in New England where DLL are common.) I have since heard that their poison is extremely powerful and know of one other person who was also bitten by a DLL.

  18. I was bitten by on my foot by something several years ago. I always assumed it was a spider. It was right on the metatarsal-phalangeal joint of my second toe on my right foot. I am fairly certain it was a spider in my tennis shoe, which I frequently threw on without socks to run outside. We saw various spiders all the time, in and out of the house, they don’t bother me much. First it just was itchy, then red, then swollen, looking like a large mosquito bite, bluish and bruised in the center. 2 Days later, I was at urgent care, with a temp of 103.4, a red line up to my knee, and couldn’t put weight on the foot. It was extremely painful, swollen…felt like someone was holding a lit cigarette to the bone, it hurt/burned from the inside out. They diagnosed cellulitis, and 5 days of IV Rocephin, rest and crutches did the trick. It was then that I learned from local vector control that the brown recluse doesn’t live here. Because, naturally, I assumed it was the nastiest of spiders 🙂 I also learned how bad cellulitis can get, so I still tell friends to keep an eye on that bite, take pics daily, measure the size, and watch for signs of infection.

  19. I completely agree here. Even though there are not many fatalities in US due to spider bites but still we need to know how to prevent it and treat it, else one might face serious consequences.

  20. Yes, I was bitten several years ago and then developed advanced arthritis especially in my knees. Last year I had double knee replacements. Two months ago my husband was bitten and within a week or two began complaining of achy joints. I believe there is a connection that has yet to be acknowledged.

Comments are closed.