Hurricanes are making spiders more aggressive: It's rapid evolution at work, study says

In the wake of natural disasters such as hurricanes, some spider populations are becoming more aggressive.

According to a peer-reviewed study published in Nature Ecology and Evolution on Monday, damage from extreme weather events such as hurricanes are creating habitat changes that affect animals in those areas.

Researchers found that as a result of these weather events, one spider species, Anelosimus studiosus, has begun to evolve because of natural selection, according to the study.

The study showed that hurricanes decrease the populations of flying insects, so there is less available food for spiders, Jonathan Pruitt, the research chair at McMaster University and study lead author told USA TODAY.

That means the remaining populations need to be able to attack quickly and effectively. Therefore, the aggressive spiders were more likely to survive in the long term.

The spiders are not aggressive towards humans, rather in their own environments for survival purposes.

"It seem hurricanes are a bombastic example of a strong evolutionary event," Pruitt said.

Hurricanes this year: The hurricane season has been rather quiet. Will it last?

Natural selection is the process by which evolution happens. Species genetically adapt to their changing environment, or they don't. The species that adapt survive and reproduce. Then their altered genes are passed down generation to generation.

"We haven’t observed spiders evolving in front of our eyes in this study," David Fisher, one of the study authors told USA TODAY. "We have measured selection induced by (tropical) cyclones; selection is a key part of the evolutionary process."

Pruitt said that what's happening is rapid evolution. With strong natural selection, you can see changes in populations over just a few generations."The average individual (spider) in the next generation is more aggressive," Pruitt said.

Along the Gulf and Atlantic coasts of the United States and Mexico, multi-female colonies of this type of spider lie in the path of tropical cyclones during the summer and fall.

(A "tropical cyclone" is an umbrella term that includes all tropical storms and hurricanes.)

The population spins their webs in branches overhanging bodies of water such as streams and rivers. They are characterized for their behavioral shifts between docile and aggressive tendencies.

Colonies that are more aggressive are better at securing resources; they're faster, more adept at capturing prey and reproduce more. They are also more prone to infighting during food shortages or other issues facing spider colonies.

Their tendencies can be triggered by what's happening in their habitat. So, the researchers asked: Have hurricanes changed colony behavior?

Researchers have looked at the effect that cyclones have on animal populations before but not in this manner, David Fisher, one of the authors of the study, told USA TODAY.

"There is a kind of level of rigor not normally associated with people studying natural disasters because most of the time, you don't predict them," Fisher said.

With hurricane season though, they were able to predict upcoming storms and replicate their observation process for the study. They also looked at the relationships across counties and the number of cyclone strikes over the past 100 years, Fisher said.

"Aggressiveness of the spiders in them is consistent with the spiders having evolved to be more aggressive in response to a higher incidence of cyclone strikes in those regions," Fisher said.

Buy climate-friendly plane fuel: Lufthansa offers customers opportunity

Scientists are concerned: Thanks to climate change, parts of the Arctic are on fire

The team studied 240 colonies in hurricane-hit areas over the 2018 hurricane season. Fisher said that Pruitt followed the spider colonies over three storms during that period.

Researchers studied spider populations before and after the storms, noting which colonies were behaving aggressively.

The team determined that hurricanes are a driving factor behind the spider population's evolution. The populations that were less aggressive were simply being wiped out during and after the storm.

While aggression may have helped spiders survive, it certainly didn't guarantee it, Pruitt said. Being more aggressive won't keep the branch supporting a spider's web from snapping in the wind, for example.

This study is only the beginning, Fisher said.

"If our goal is to anticipate future conditions of the planet, we have to get a handle on what these extreme events do," Pruitt said. "It might turn out that hurricanes are great for organisms, but we don't know whether that is true or not."

Follow Morgan Hines on Twitter: @MorganEmHines.

This article originally appeared on USA TODAY: Spiders becoming more aggressive to survive after hurricanes