Black widow spiders are now creeping farther north than ever before.
A new study using observations from citizen scientists found that the notorious arachnids have expanded their northern range since the 1960s, pushing increasingly toward Canada.
The shift is likely linked to climate changes over the last few decades, with temperatures during the hottest months of the year thought to be a major driver of their activity.
Black widow spiders are now creeping farther north than ever before. A new study using observations from citizen scientists found that the notorious arachnids have expanded their range since the 1960s
In the study published to the journal PlOS One, researchers from McGill University created an updated species distribution map using citizen science contributions to online databases, and museum collections.
The team investigated two spider species: the Northern black widow (Latrodectus variolus) and the Black purse-web spider (Sphodros niger).
Using statistical tests and modelling tools, the researchers plotted a current range for the two species.
Then, they compared this to the historical data, revealing how the two have shifted.
According to the team, purse-web spiders appear to have expanded their range to the north, while their distribution in the US southwest has declined.
Black widows, too, appear to be pushing toward more northern states and Canada.
‘Our models show the first reliable distribution maps of these two species,’ the researchers said.
‘The logical next step is to conduct sampling efforts in typical habitats associated with these species in our predicted range to further validate the models.
‘We propose to call on citizen scientists by launching a monitoring project through a platform such as Bugguide and iNaturalist to produce a large-scale sampling effort.
‘This would represent a rapid, low-cost, highly efficient, and innovative way to test these large scale predictive models.’
According to the team, purse-web spiders appear to have expanded their range to the north, while their distribution in the US southwest has declined. Black widows, too, appear to be pushing toward more northern states and Canada, as shown in the map above
The researchers say climate was a major factor in predicting the spiders’ current range.
For the purse-web spiders, the mean temperature of the coldest three months was most important for where they might be found.
For black widows, on the other hand, the mean temperature of the warmest three months was most significant.
IS A FEAR OF SPIDERS IN OUR DNA?
Recent research has claimed that a fear of spiders is a survival trait written into our DNA.
Dating back hundreds of thousands of years, the instinct to avoid arachnids developed as an evolutionary response to a dangerous threat, the academics suggest.
It could mean that arachnophobia, one of the most crippling of phobias, represents a finely tuned survival instinct.
And it could date back to early human evolution in Africa, where spiders with very strong venom have existed millions of years ago.
Study leader Joshua New, of Columbia University in New York, said: ‘A number of spider species with potent, vertebrate specific venoms populated Africa long before hominoids and have co-existed there for tens of millions of years.
‘Humans were at perennial, unpredictable and significant risk of encountering highly venomous spiders in their ancestral environments.’
The researchers say the updated maps could help to forecast the shifting range of rare species as the climate changes.
‘Distributions of spiders are relatively poorly known, and range maps are often based on just where scientists have found the species,’ Wang said.
‘Using Northern black widow spider and Black purse-web spider as examples, this paper illustrates that we can (and should) incorporate citizen science data and distribution modelling techniques to help bridge the knowledge gaps of less-studied species.’