Hurricanes help aggressive spiders spread, study finds

Aggressive spider colonies are more likely to survive and reproduce after hurricanes than more docile ones, according to new research. 

Scientists studied colonies of Anelosimus studiosus, known as the communal spider or tangle web spider, which live throughout North and South America.

They found the temperament of a colony can be the difference between life and death: aggressive colonies had a higher rate of reproduction following a tropical storm, whereas in regions with no storms, more docile colonies did better, according to researchers from McMaster University in Ontario, Canada.

The study suggests the increase in extreme weather events will have a significant evolutionary impact on populations of spiders. 

Researchers looked at spiders in the Gulf and Atlantic coast of the US, an area which is exposed to hurricanes that form in the Atlantic basin from May to November. They looked at the effects of three subtropical storms that hit the area in 2018 – subtropical storm Alberto, Hurricane Florence and Hurricane Michael.

Researchers sampled 240 colonies throughout the region and compared them to control sites, according to the study, published in Nature, Ecology & Evolution. 

They divided the spider colonies into two groups of inherited personality traits – docile and aggressive.

The aggressiveness of a colony is determined by the speed and number of attackers that respond to prey; the tendency to eat each other and how easily foreign spiders get into the nest. 

Aggressive colonies are better at acquiring resources but are more prone to infighting if they are deprived of food or the colony has got too hot. 

Scientists worked out how aggressive the colony was by vibrating the web and counting the number of spiders that attacked. 

They returned to the site 48 hours after the hurricane to see which colonies had survived and then on two later occasions they went back to see how many eggs had been produced and how many spiderlings had hatched. 

The analysis showed that after hurricanes, more aggressive colonies produced more eggs and had more spiderlings survive into early winter. Researchers found this trend was consistent across multiple storms of different sizes and duration. 

Lead author Jonathon Pruitt, an evolutionary biologist at McCaster University said: “Tropical cyclones likely impact both of these stressors by altering the numbers of flying prey and increasing sun exposure from a more open canopy layer. 

“Aggressiveness is passed down through generations in these colonies, from parent to daughter, and is a major factor in their survival and ability to reproduce.”  

He added: “As sea levels rise, the incidence of tropical storms will only increase. Now more than ever we need to contend with what the ecological and evolutionary impacts of these storms will be for non-human animals.”