Why one biologist chases hurricanes to study spider evolution

Don’t just sit there. If you really want to bring scientific rigor to studying evolution and spider aggression, drive into a hurricane.

That’s the notion that turned Jonathan Pruitt of McMaster University in Hamilton, Canada, into evolutionary biology’s storm chaser. He has rushed to the southeastern United States to collect spider data right before a storm and within 48 hours afterward. “I grew up in Florida,” Pruitt says; he knows hurricanes.

As a kid ready for a break from school, “I would always hope that our hurricanes hit during a weekday instead of on a weekend.”

Most studies of what hurricanes do to wildlife are just lemonade squeezed from the bad luck of storms that trashed some unrelated project in a forest, bird colony or other research site. An ideal hurricane study, however, needs replications and undamaged sites for comparison. Otherwise, “you just have one site where something bad happened,” Pruitt says.

What sparked him to try something different was an unusual 2018 Nature paper from researchers checking Turks and Caicos anole lizards before and several weeks after two Category 5 hurricanes blasted the islands. Survivors tended to have bigger toe pads than usual, said researchers based at Washington University in St. Louis. They proposed that bigger pads might give the anoles a better grip during high winds. Such a shift in anole survivors could be a rare sign that killer storms, even though sporadic, might count as an evolutionary force that tweaks animal traits. The researchers explored lizard behavior in high winds by aiming a leaf-blower at small, brown lizards gamely gripping poles.

That paper inspired Pruitt to set up multiple pop-up research sites just days before a storm strike. As hurricane Michael barreled toward Florida in October 2018, for instance, Pruitt dashed from Canada to set up headquarters in Macon, Georgia, roughly between two groups of spider sites. To see heavy damage, he picked spots nearer the coast, and for comparison sites facing less risk, he chose places in the Florida panhandle.

“Even Macon got hit by a Category 2,” he says. Downed power lines and trees blocked roads, so getting back to the test sites “was a bit of a kerfuffle.”

What saved the project were the people in the rural communities who rush out to explore roads and post damage pictures to Facebook. “Every single person, including me, has a giant pickup truck, and unlike me, they have chainsaws,” he says. Often a group would carve a path for him because “they think it’s funny that someone would be out there studying spiders.”

The social spiders he studies are “tiny little brown things,” he says. These comb-footed Anelosimus studiosus “don’t start trouble with anybody, unless you’re prey snared in their web.” When a fly or other prospect bumbles into the web, some colonies react more aggressively: Five or six spiders swarm toward the victim, instead of just one or two (SN: 4/21/12). To quantify aggression, he counts the initial party. To mimic flailing prey, he sticks a bit of paper to the web and makes it flutter with the touch of an electric toothbrush.

Colonies, aggressive or meek, died at random during storms. But post-storm, the more aggressive ones fared better in the damaged landscape, Pruitt and colleagues report August 19 in Nature Ecology & Evolution. The most aggressive surviving colonies were more likely to have more offspring in the storm year than timid colonies did. In a 100-year historical view, spider colonies were more aggressive in counties hit by more hurricanes than in places hit by fewer such storms. “It’s only a minor signature, but a signature nonetheless,” Pruitt says.

Picking last-minute comparison sites as the spider researchers did is “a really, really powerful technique,” says evolutionary ecologist Colin Donihue of Washington University, who worked on the Caribbean lizards. Pruitt will be heading to Australia in hopes of an even livelier season of cyclones.