Saturday, March 9, 2013

Ask An Expert: Brown Recluse Spiders in BC

 Hobo Spider (Tegenaria agrestis), photo by Robb Bennett.
Not so fearsome as thought.


 "You state on your site that there are no Brown Recluse Spiders in B.C.  I have a friend in Duncan bitten on the foot which was diagnosed as Brown Recluse bite... [and]...I know a fellow in Kelowna that was bitten a couple years back and he had the inside muscle on his lower arm taken out in the hospital, wrist to inner elbow...he was also diagnosed as Brown Recluse bitten............What is your response? Do we have a clone here in B.C.?.....submitted by Jamie

Dear Jamie,

It is certainly unfortunate that your friends have suffered disfiguring and debilitating medical conditions. 

It is also unfortunate that a small minority of medical professionals apparently continue to provide erroneous diagnoses of brown recluse spider bite in the absence of any credible evidence.  If an appropriate diagnosis had been made your...friend’s foot would almost certainly have healed ages ago and your.... buddy might not have had to have muscle tissue removed. 

Although I cannot diagnose what sort of medical conditions your friends have suffered, their conditions were definitely not caused by bites from brown recluse or other spiders. 

Over the last 20 or 30 years a large number of peer-reviewed articles published in professional medical journals, ranging from Canadian Family Physician to Lancet and the New England Journal of Medicine, have completely debunked the popular mythology surrounding brown recluse spiders and their bites, including establishing the following facts:
  • it is very rare for anyone to suffer a bite from a brown recluse spider, even in areas of North America where they are very common 
  • most true bites never result in medically significant issues 
  • it is exceedingly rare for a bite to cause tissue necrosis 
  • nearly all medical conditions that have been blamed on bites from brown recluse or other spiders are actually caused by other medical conditions completely unrelated to any sort of spider 
  • the medical conditions that have been mistakenly diagnosed as resulting from brown recluse spider bites are numerous and range from simple chemical and radiant heat burns, through antibiotic-resistant bacterial infections and flesh-eating diseases, to syphilis, various cancers, and anthrax 
  • erroneous diagnosis of a medical condition as being the result of a bite from a brown recluse or other spider usually results in inappropriate treatment which can delay healing and/or cause unnecessary suffering even to the point of death 
  • brown recluse spiders are not often found outside of their natural range in the south central United States and definitely do not occur anywhere in or near Canada.
I urge you to take the time to learn the facts about spiders and share the knowledge with your friends and their doctors.  Forget the mythology – no one needs to suffer as your friends apparently have.  

A few good websites that will help bring you up to speed on spider bite facts and fiction are listed here:    

  • Rick Vetter’s spider research website is absolutely the best place to find anything you need to know about brown recluse and other spiders of real or imagined medical importance - 
  • Colorado State University’s  “mystery bites and itches” website provides an excellent review of all sorts of beasts that have been fairly or unfairly blamed for causing medical concerns in humans.  The spider section is especially good. 
  • Finally, Rod Crawford’s “spider myths website” provides a good overview of a wide variety of myths and misinformation associated with spiders -
I sincerely hope that the information I have provided here is helpful to you and your friends. 

Robb Bennett, Ph.D., F.E.S.C.
Research Associate, Entomology 
Royal BC Museum


  1. Way to go, Robb. Thanks for the facts.

  2. I am happy to hear this b/c I just caught a gross little critter this morning that looked I realize after looking around I am in no way expert enough to determine what it is...harmless (but ugly) typical house spider I imagine.

  3. I had a bad infection from a spiderbite. Some people said it was from a poisionous spider but it actually was just that I had MRSA (a super bug). Im sure I would have been fine otherwise. I had cellulitus (infection of the cells) and a large pocket of infection. I had surgery and was only left with a scar the size of a loonie.

  4. Dear Gwen - thanks for your positive comment and I am happy that you
    have had a successful recovery from your MRSA infection. I note, however,
    that you feel that the original source of your infection was a bite from a
    spider. This is extremely unlikely - bites from spiders are not known to
    result in bacterial infections. Although I have no doubt that your
    diagnosis of, and subsequent treatment for, MRSA infection were respectively
    accurate and reasonable, the initial source of your infection was something
    else other than the bite of a spider.

    Sincerely and with best wishes,

  5. I'm wiling to accept it's not a brown recluse because we are out of their natural range, and unlikely to be a hobo, or any other arachnid, but...I'm 72, don't have diabetes, VD, infections, or any other known problems (don't take any drugs for anything, don't even have an aspirin in the house). With that in mind, to what then, in your opinion, should I attribute waking up around 5 in the morning after the evening before leaning against the near row of the woodpile to reach the further row, with a 1/4 inch high bright red cone and surrounding 3" diameter red ring. Three hours later, the cone had a dark brown cap, the ring had progressed to about 5 inches, and there were red lines snaking out in all directions. Six hours later, the cap was black, the ring was close to 8 inches in diameter, and there were pustules forming. I checked the bed and there were no body parts or smears on the sheets. The location of the eruption was side of groin, the same height as the lower row of the woodpile.

    The Doc gave me a tetanus shot, and sent me off post haste to the hospital for a combination pills/iv antibiotic treatment for a minimum of 7 days, then review...

    By the second day the pustules had broken and there were craters instead, and the ring was now out to 10 inches. Day three, the red had reduced slightly to 7 inches in the morning, but was back up to 8 by evening. Day 4, the ring a.m. is down to five inches, pustules are mostly broken, craters all around the cap, the whole thing starting to itch slightly..

    I'll be dealing with the hole later. In the meantime, I haven't had a day off work for sickness for five years. The Doc says I'm disgustingly healthy, regardless of age. I can't find any other insect that's a likely culprit, and am hearing stories locally of others with identical symptoms. If it's not an arachnid, what is it?

    Sally T.

    PS: zero pain. Much like a bruise, it;s only is tender if I touch it.

  6. You are right to assume that your affliction was not caused by a bite from a spider. There are a great many medical conditions that could express themselves with symptoms the same as, or similar to, the ones you have experienced, all of which are much more likely to have caused your affliction than a spider bite.

    At this point, a causative agent is not likely to be identifiable. If your doctor is unable to identify the cause after examining you, there is not much else that can be done. I am not a medical professional and cannot diagnose your condition.

    You may find the information posted at the website to be of interest. Although it is written for the central western USA area, much of the information is relevant to BC as well.

    I wish for you a speedy and uneventful recovery.


  7. sounds like a tetanus infection :)

    No brown recluses in Canada people.

    Not frost tolerant, Locally abundant where they occur, but show me one, any one, you should be able to find a few dozen, but you wont, because they don't tend to establish populations outside of their range.

    There's also o legitimate reason to assume Hobo spider bites are medically significant either, in fact the simple science disputes it. Tegenarism has never been described in the animals native range. period. That's because doctors in those regions haven't thought to cut diagnostic corners and
    scapegoat that spider yet.

    Mitch Guilderson

  8. Thanks Robb!
    I have worked as a physician in BC for a number of years and find that spiders get a bad rap from both patients and my colleagues for things they have nothing to do with. Cellulitis, abscesses, joint infections MRSA get blamed on spider bites. "I didn't see the spider doc but look at it. It must have been a brown recluse". MRSA lesions in particular often get a small scab or two on the top that can look like a bite mark. It's not. These things are usually due to simple bad luck. Thanks for helping to dispel this common myth.

  9. I'm the first to defend spiders. In fact, to understand them better and get over my typical human fear of them, I adopted a tarantula (now I have a whole other take on pet exotics, but that's another story). Talk about getting a bad rap! There is no record of a tarantula ever killing a human being (unless they were unfortunate enough to have an allergic reaction, as with bee sting). Additionally, we have a string that lowers into our bathtub to allow spiders that fall in to climb back out. That said, I am here writing this now because I am visiting BC and noticed a painful, hard blister with a darker central speck on my finger yesterday with surrounding erythema. On closer look, there were two tiny puncture wounds, about 2 mm apart, each with own blister. I don't recall a moment where I was bitten by anything, though I had been gathering wood for a fire and felt a little nauseous for a couple hours late yesterday afternoon with no real explanation. At first I considered a splinter, soaked my finger, then unroofed one blister. Nothing came out--no pus, blood, or other fluid, nor any object--only the area became peppered with little pinpoint blood spots (petechiae) immediately. I left other one alone. Then washed well, more warm soaks, applied topical antibiotic, no bandage. It's about the same today. My next thought (after splinter) was that it was and insect or spider, but I was not familiar with BC species, so I did an internet search and found this site. My husband, (a former ER doc turned organ transplant specialist), is in the states right now or I'd have him take a look. My question is this: could you please inform us of what spiders or insects actually ARE venomous in BC? Or is there a website you could direct us to which explains this and what signs/symptoms to look for so we could all be better informed? thank you.

  10. Thanks for your query.

    With respect to your questions: Among the over 800 (and counting) spider species that are known to occur in BC, only our native black widow spider species, Latrodectus hesperus, produces a venom that can have serious medical implications for people who are unlucky enough to be bitten by one. Fortunately, however, black widows are extremely unlikely to bite humans and it has been a great many years since I heard of anyone in BC or elsewhere in Canada suffering a verified black widow spider bite. Among BC’s myriad insect species, some (e.g., a variety of bees and wasps) can inflict a painful venomous sting but none, however, are considered to be dangerous to humans except for those few folks who, as you say, are unfortunate enough to suffer a severe allergic reaction.

    With respect to the lesions on your finger: It is highly unlikely that you were bitten by a spider – in fact, I will go so far as to say that you were not bitten by a spider. You may, perhaps, have suffered a minor reaction to a bite or bites from a blood feeding insect such as a flea or a bed bug, or to a sting from a wasp or bee (although there aren’t yet many of those about at this early date in the spring). Or your lesions may be the result of some other factor not related to any bite or sting. In the absence of any actual beast that you witnessed biting you, the latter explanation is the most likely.

    I wish you a quick recovery and urge you not to blame spiders for strange lesions of uncertain origin. There are many other, much more likely causes for strange lesions. You may find the information about “mystery bites and itches” in the following website of some use: Although it is written for a west central USA audience, the information is broadly relevant for most regions of North America. Rick Vetter, at University of California Riverside, has much information available regarding spider bite mythology; check out his website at Catherine Scott, at Simon Fraser University, maintains a very readable blog about spiders and one of her recent articles (co-written with Chris Buddle at McGill University) deals with spider bites:

    Finally – KUDOS to you for defending spiders and helping them out of your bathtub. It is great to meet yet another member of the public who thinks that spiders are as fascinating and wonderful as do we professional arachnologists.

    Sincerely and with best wishes,



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