Paul Hetzler
The Advocate
Spiders can be dangerous in weird ways. In 2014, Mazda had to recall more than 40,000 vehicles because yellow-sac spiders liked to plug fuel-vent lines with silk and nest inside them, causing gas tanks to pressurize, leak and cause fires. In that same year, a guy in Seattle burned his house down trying to kill spiders with a blowtorch in the basement. And at a Michigan gas station in 2015, a man tried to kill one with a lighter and torched a whole pump island.
But fire isn’t typically why we fear spiders.
Some experts think our aversion to spiders may be an evolutionary response, woven into the very strands of our DNA. Even though fewer than 1 per cent of the world’s 50,000 species of spiders pose a risk to us, early humans who kept their distance from things like spiders, scorpions and snakes probably lived longer.
These days, fake spiders star in horror films and come out of the woodwork at Halloween time because a lot of folks – perhaps 75 per cent of the population – still find them creepy. Arachnophobia, an intense fear of spiders, affects 3 to 6 per cent of us worldwide, and is the most common phobia among humans.
I want to point out that spiders are essential to the web of life, eating millions of tons of insects each year. They reduce fly populations in barns tremendously, and a 2023 University of Guelph study found that spiders are key predators of agricultural pests like aphids. Even though they’re beneficial on the whole, it’s good to know how to identify and avoid the few poisonous spiders that live in our climate.
Canada is home to roughly 1,400 kinds of spiders, of which at least 70 are invasive. At the moment, we only have one species that is truly dangerous, and another two that are mildly toxic. The northern black widow is the main species of concern. In spite of its name, there’s a limit to its cold-hardiness. This native spider occurs in the southern portions of five provinces, including Quebec, where it has been found as far north as Montreal. However, based on a survey done in 2018, researchers from McGill University believe it is slowly moving northward due to climate change.
Here’s one to watch out for
A red-and-black colour scheme on a car is sporty. On a spider, it’s scary. Lucky for us, to identify the northern black widow we don’t have to flip it over to look for the characteristic red hourglass shape on her belly. Females, whose bodies are only nine to 11 millimetres long, can measure 25 to 38 mm when you include the legs. Males are half this size. Females have red geometric shapes (often like a “broken hourglass”) on their dorsal sides, and a red hourglass on their bellies. Males are harder to identify, as they can have stripes or spots in either red or white.
An interesting sidebar about black widows, so called because they’re known to eat the males after mating, is that such behaviour is not the norm. This “sexual cannibalism” was first seen in the lab where males couldn’t get away. It seems that in the wild, males have a “best defense is a running head start” policy, and most survive.
Fortunately, black widows live outside. But they sometimes come in on firewood or other items on which the shy, nocturnal bug-hunters hang out during the day. Northern black widows can also wander in through gaps in foundations or broken weather-seals around doors if there are cool, damp places next to the house to hide in. Move brush and leaves away from foundations, and keep door gaskets in good shape.
Their bites initially cause redness and swelling, followed by severe muscle and stomach cramps, nausea and sweating within an hour. If you’ve been bitten by a black widow, call a poison control centre or dial 911 immediately. Apply ice to the bite while you wait for help. Do not use a tourniquet.
And one more to beware
Although black widows have the most toxic venom, the brown recluse spider has caused more deaths. Bites from the brown recluse, while rare, may require medical intervention because they can result in extensive tissue death (necrosis), with possible infection and scarring. In about one per cent of cases, their bites are fatal when the venom becomes systemic.
Brown recluse spiders are shiny, hairless, tan to brown, and up to a half-inch long. An important feature to look for is a dark brown, violin-shaped mark on its back, with the neck of the violin pointing backwards. True recluses, these guys like sheltered places, which is a problem when they hide in clothing or bath towels. Primarily an outdoor species, brown recluse spiders will adapt to living inside. The thing is that they sometimes stow away in luggage or gear of returning snowbirds – brown recluses are common in the southern U.S.
Most brown recluse bites result in tissue death around the bite, forming a wound that can take months to heal. The main concern is infection at the site. Bites that lead to fever, nausea or dizziness may suggest a systemic response, and you should seek medical care right away.
We do have two species of house-dwelling, slightly toxic spiders that can bite, the yellow-sac spiders. They can reportedly survive almost up to the Arctic Circle, so it’s a sure thing they’re in your region. Ghostly pale, almost translucent, yellow sac spiders actually range in colour from yellow to greenish, or occasionally pink or tan. They’re tiny; just eight to 10 mm long, which makes them easy to overlook.
Yellow sac spiders cache their silken sac-homes in nooks and crannies behind pictures, in the corners of rooms and, apparently, in auto fuel vent lines as well. Though not dangerous, this species has a mildly toxic venom that causes a rash, and sometimes a limited necrotic area.
About 30 years ago, one bit the side of my neck (it was in my shirt collar), and a nickel-size wound developed. The lesion turned grey, and took nearly a month to heal. I have to count my blessings, though. There was no fire.