To the list of things we’ve learned to fear from hurricanes — high winds, storm surge, floating islands of fire ants — a new study in the journal Nature Ecology and Evolution suggests that we should add another: aggressive spiders.
The study, which looked at more than 200 colonies over roughly a dozen places in the paths of hurricanes, found that more aggressive spiders were more likely to survive once a storm had passed.
Anelosimus studiosus is a type of communal living spider found along the Gulf and Atlantic coasts of Mexico and the United States. They’re small, stretching slightly less than a quarter of an inch fully grown, and scientists like to study them because their colonies exhibit one of two distinct behaviors.
Some Anelosimus studiosus colonies are relatively docile, with multiple mothers rearing each other’s offspring, gathering food together and otherwise sharing the work necessary for survival. Other colonies, however, are more combative and feature a higher ratio of aggressive female spiders.
“Aggressive females are great at capturing prey,” said Jonathan N. Pruitt, an associate professor in the department of ecology, evolution and marine biology at the University of California, Santa Barbara, and an author on the study. “They are really good at defending the colony from intrusion by other species of spiders.”
“But they can’t really seem to turn off their aggression,” he added. “So, sometimes they mistakenly kill their young and sometimes they mistakenly maim one of their fellow colony members.”
Dr. Pruitt’s research suggests that filicidal spider colonies fare better after hurricanes.
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He and his colleagues determined that hurricanes were shifting spider behavior after surveying colonies in regions that were hit by hurricanes immediately before, immediately after and then several months after storms struck. Right after a storm, the team found no significant shift in a colony’s behavior. But when the researchers went back months later, they found that of the colonies that remained, more of them were aggressive. The researchers measured aggression by placing a piece of fluttering paper near a spider web and seeing how many female spiders emerged to attack it over a two minute period.
“The study was about spiders, but the implications are much broader than that,” said Matthew P. Ayres, a professor of biological sciences at Dartmouth College who was not involved in the study. Spiders aren’t the only animals to exhibit this kind of behavioral split where some groups are aggressive and others are more docile. Climate change is expected to increase the impact and severity of hurricanes so this effect could potentially extend to other animals.
Since the researchers couldn’t predict which specific areas were going to be hit by hurricanes, Dr. Pruitt had to fly into regions after a hurricane warning had been issued, but ahead of the storm, to get baseline data. And, once he got it, he had to stay in the region to revisit the surveyed colonies within 48 hours after the hurricane departed.
“I would not have been able to get back to some of my study sites had it not been for this surge of camaraderie that emerged following tropical cyclones,” said Dr. Pruitt. He noted that people were using chain saws and their trucks to basically break apart trees, “so that I could get closer to my site and so they could drive around and check on their neighbors.”
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