Citizen Scientists Show Black Widows Creeping North In Canada

Study shows online observations can help researchers refine the range maps of many species overlooked by field biologists

Northern Black Widow
Northern Black Widow Sean McCann

To humans, 31 miles may not seem like a very long distance to travel, but for a spider, it’s a long, long way to go. Emily Chung at the CBC reports on a new study that shows that since the 1960s, the northern black widow spider, Latrodectus variolus, has crawled that much further into Canada and may continue skittering northward as the climate changes.

Thanks to lead author Yifu Wang of McGill University and her team’s efforts to use citizen-scientist data to create updated range maps of the much-feared species, we now know the black widow has moved into new territory.

Most of what we know about the ranges of insects—and really most species—comes from field biologists tramping through nature, collecting specimens and noting the species they see. But it’s a big world out there, and field biologists are few and far between, so range maps—especially for small or obscure species—are just best guesses in many cases. Granular data is important now, perhaps more than ever before, as global warming reshuffles species across the globe.

As Wang’s team demonstrates, tapping citizen scientists could be a useful way to improve range maps. In the last decade, digital tools have allowed nature nerds across North America to log sightings of plants, birds, insects, mammals and more using platforms, like eBird, iNaturalist, BugGuide and others.

For this study, the researchers looked at citizen-science data from iNaturalist and BugGuide as well as newly digitized museum collections across the continent to plot the range of two species, the northern black widow and the black purse-web spider, Sphodros niger. Using statistical techniques, they excluded questionable sightings to create predicted range maps. They then looked at historical range maps to see if the spiders had made any moves in recent decades. The results are the first reliable range maps of both of these species.

“Distributions of spiders are relatively poorly known, and range maps are often based just on where scientists have found the species,” Wang says in a statement. “[T]his paper illustrates that we can (and should!) incorporate citizen-science data and distribution modeling techniques to help bridge the knowledge gaps of less-studied species.”

One reason the team chose black widows is that the markings on the spider are quite distinctive, making misidentification less likely. Though the study was primarily a test case, it did yield some new data about the black widow. Compared to pre-1990 data, it appears that the species is slowly but surely marching northward, most likely as a response to climate change. That means it could be possible to find the spiders in Montreal, a place they have yet to be discovered. “They’re occupying new habitats that we didn't previously think they could,” Wang tells Chung.

And what should you do if a black widow does take a stab at you when you’re reaching for some poutine or perhaps logging a sighting in iNaturalist? Typically the bite causes pain at the site, which can spread to the abdomen or chest along with severe cramping and excessive sweating. The bite is rarely fatal for healthy adults, but everyone—most importantly children and the elderly—should check in with the doctor after an encounter.

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