Last week, the arthropod lab was lucky enough to be highlighted on the website “Montreal Openfile”. When discussing our work with spiders as related to McGill’s spider collection, I was asked about the most common misconception about spiders, and I responded quickly with the following:
There are a lot of misconceptions about spiders. The most common is the idea that spiders frequently bite people – they do not. Most so-called spider bites are caused by something else. Spiders generally have no interest in biting us, and would rather feed upon invertebrates. I have been working with spiders for over 15 years, and I have handled many, many kinds of live spiders and I have never been attacked by a spider.
It is really quite astounding – almost anyone you talk to seem to know someone who has been bitten by a spider and/or they themselves have a personal story about a spider that bit them. These stories often include anecdotes like “it really, really hurt“, “the wound swelled up and festered“, “I was bitten over and over again in the middle of the night“, “the spider ran right at me and bit me” etc. Related directly to this are the numerous questions I get about the brown recluse spider, and its occurrence in Quebec. If I believed everything that people told me, I would NOT be an Arachnologist, and I would fear for my life – Venomous spiders everywhere!!!
Time for a reality check – Spider bites are very, very rare and other more likely causal factors should be given priority. Let me go into detail:
1) Misdiagnosis: other animals are more likely to be the cause of so-called “spider bites”. The usual and more likely suspects include things like wasps, ants, bedbugs, black flies, etc. Message: these kinds arthropods are known to sting, bite, or “feed” upon mammals! (…and reactions to some of these can certainly be severe, and serious). How do I know that spiders rarely cause reactions in humans? Two reasons: experience and the scientific literature (i.e., evidence or lack thereof). For example, a few years ago colleagues of mine (Robb Bennett & Rick Vetter) wrote about this in a paper for Canadian physicians:
There are two key pieces of information in this article: first, the medical community must recognize the possibilities of other likely causal factors for symptoms sometimes attributed to spider bites. Second, to properly verify a spider bite, the spider needs to be collected and properly identified. This takes me to the next point – the importance of taxonomy.
2) Incorrect identification: Several years ago a woman approached me after a pest-control company sprayed her home – she brought me specimens of the ‘deadly’ spider that they had sprayed for. It was NOT a dangerous spiders – it was a completely harmless wolf spider (Family Lycosidae) from the genus Trochosa. She saw a spider, called in the professionals, and these professionals did not accurately identify the spider (they told her it was a brown recluse). TAXONOMY IS IMPORANT and TAXONOMIC EXPERTISE is essential. It is critical that a careful identification is done (by an expert!) on any spider that supposedly bites someone. In my experience, a casual image search on the Internet will not suffice, and will likely confuse the situation, and perhaps cause undue alarm. [as an aside, this blog post about ‘the taxonomy fail index’ is worth a look]
3) Spider behaviour: Spiders are “scared” of humans. Ok, I recognize this is anthropomorphizing things, but the reality is that if you approach a spider, it usually runs away, or completely ignores us. With the exception of jumping spiders, most spiders have very poor eyesight and respond to other stimuli (e.g., vibrations, light/dark). Humans make a lot of noise, and cause a spider’s entire habitat to shake, rumble and roll. Furthermore, spiders prefer to live in damp, dark places, and when we lift up an old shoe box, or sweep under the fridge, we sometimes disrupt a spider but if you wait a minute, they invariably run back to darkness. Spiders would rather run and hide than hang out with us.
4) Home range: Venomous spiders (i.e., to humans!) just don’t live in Canada. Of the almost 40,000 spider species, globally, there are less than a dozen or so that can cause serious health problems to the average, healthy human, and these do not occur naturally in Canada (Australia, however, is a different story!). One of the authors of the paper mentioned above (Rick Vetter) has a terrific website devoted to the “myth” of the brown recluse. Also, his list of publications will take you to some key literature on the broader topic of medically important spiders. Rick has put together a terrific map showing the distribution range of the brown recluse, and I’ve copied it below. As you can see, Canada is not part of the native range of the brown recluse (or its close relatives):
5) Spider food: Spiders prey upon invertebrates and for the vast majority of spider species their venom is suited for invertebrates. Their venom can certainly pack a punch, but it is generally not suited for vertebrates (at least certainly not in northern climes, there are spiders elsewhere who do prey upon birds, for example).
6) Biological constraints: For many species, the “fangs” of spiders (which are located at the end of the Chelicerae) are just too weak and small to be able to break the skin. I have held many spiders and watched as they work away at trying to bite me, but they just can’t pull it off. Our skin is generally too tough for their little, wimpy fangs. Here’s a photo to show this (it’s another wolf spider, trying unsuccessfully to bite me):
To summarize this rather lengthy post: in general, and in this part of the world, venomous spiders are rare, and bites from venomous spider bites are exceedingly rare, and I would argue that most suspected spider bites are not actually caused by spiders. The risk of a spider bite is very, very low. If you want to reduce risk, it’s far more dangerous to get in a car than be bitten by a spider.
Writing this post has inspired me to think about other misconceptions about spiders. Stay tuned…there’s a lot more to come!
