Saturday, April 15, 2023

The much-maligned spider

The Globe has published an excellent article today on disinformation about spiders, entitled, perhaps inevitably, Web of Lies.

Long before disinformation campaigns on vaccinations or stolen elections, spiders were already the subject of an apparently concerted attack and smear campaign. Starting with the regular appearance of the northern yellow sac spider (Cheiracanthium mildei, a common basement and stairwell spider here in Canada) on lists of Top 10 Most Dangerous Spiders, there are any number of false allegations about spiders out there that have helped make arachnophobia the single most popular bio-phobia (a fear of things in nature), affecting between 3% and 11% of the population, depending on definitions. The world, as the article notes, is "teeming with bad spider science".

No, spiders do not lay eggs under your eyelids (or anywhere else on your body, for that matter). Sleeping humans do not eat up to eight spiders a year, as the urban myth has it. If you find a spider in the sink or bath, it hasn't maliciously crawled up from the sewer with intent to harm; it has almost certainly fallen in and can't get out. While spiders do have an alarming number of babies, typically only a couple live to adulthood. And, no, they don't drink blood (and so have no reason to bite us, unless severely goaded and in danger of their lives).

The press has a lot to answer for, of course, with its sensationalized articles taking advantage of already exaggerated preconceptions about spiders. One study found factual errors in 47% of news articles about spiders, and 43% were sensationalized in tone or details (and, of course, the more sensationalized, the more they were copied and disseminated). A recent newspaper article in the UK, for example, described a woman - and yes, it is usually a woman! - with an oozing red bite on her wrist, who "could have died" from the false black widow spider bite, despite the completely lack of evidence for the presence of that particular species, and the fact that no-one has ever died from a false black widow bite.

And the reputation of the yellow sac spider? It appears to owe its notoriety to a 1970s paper in the American Journal of Tropical Medicine, which suggested that the spider caused necrotizing bites. That article turns out to have looked at the effect of multiple spider bits on guinea pigs, following some unspecified and inconclusive reports in the Boston area. The paper concludes that "more research is needed", but somehow nevertheless became one of the most oft-quoted spider papers ever. (In fact, if a human is bitten by a yellow sac spider, it causes a bit of an itch and a red mark the size of a dime that disappears the next day.)

Yes, there are some dangerous spiders around, although their numbers and their threat are exaggerated. Of the approximately 51,000 species of spiders worldwide, only 0.5% are "medically significant" to humans. And they are really not interested in biting us. Over the past 10 years, the American Poison Control Centre shows only three recorded fatalities from spider bites, two of them attributed to the brown recluse spider (a species, incidentally, not found in Canada). One American researcher collected 2,055 brown recluse spiders from a single house in Kansas, but the resident family of four humans had shared the space for years without incident.

Even a black widow spider bite, although serious, is rarely fatal. Typically, it results in pain around the puncture spot, some flu-like symptoms and sweating for two or three days, and complete recovery by Day 5. Not pleasant, but in the scheme of things...

One place to take spiders very seriously is Australia, where the funnel web spider, one of the deadliest species in the world, bites about 40 people a year, and the redback spider (almost as venomous) upto 2,000 a year. But, even in Australia, there have been no verified deaths from confirmed spider bites since the 1980s, i.e. since the invention of widely-available venom antidotes. Interestingly, Australians are less fearful of venomous spiders and snakes than Europeans and North Americans, despite - or maybe because of - having many more (and more dangerous) species to deal with.

The bottom line is that spiders are voracious consumers of flies, mosquitoes and bugs, without which human life would be much worse. And any spider-human encounters are unlikely to present any danger. The fangs of many spiders are too small or flimsy to pierce human skin, and their venom not sufficiently toxic to present a danger to us hulking humans. And, quite honestly, they are just not interested, and have better things to do with their time.

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