Spiders, like humans and many other species, have their own distinctive characters that help to shape their individual lifestyles, a new study suggests.
Depending on the type of spider, the personality differences could help to predict whether the individual frequently pounces and attacks or is more likely to calmly sit around and observe.
"The main personality measure that we used in our study was termed ‘boldness' and was measured on a continuous scale, meaning that individuals could be found at any point of the scale from very shy to very bold," lead author Lena Grinsted of Aarhus University's Department of Bioscience told Discovery News.
For the study, published in the latest Proceedings of the Royal Society B, Grinsted and her team focused on the social spider Stegodyphus sarasinorum. Out of the more than 44,000 known spider species, it is one of only about 25 species that live in groups where members cooperate with each other.
"The vast majority of spider species live solitarily and are highly aggressive towards other spiders, even of the same species," Grinsted said.
Even these solo operators probably have their own personalities, but for comparison, researchers Grinsted, Jonathan Pruitt, Virginia Settepani and Trine Bilde looked at S. sarasinorum female colony members that work together to handle common tasks. Those include duties like prey capture, feeding, brood care and building and maintaining the silk nest and capture web.
These spiders are impressive when capturing prey, such as big grasshoppers or beetles, which are more than five times their size. The female spiders will often cooperate in subduing the victims in the web.
The first females to run out tended to be the biggest, but size had no influence on whether they would attack. The boldest spiders would tend to be the attackers.
"We do expect that shy spiders that do not help out in prey capture do specialize in other group activities, such as brood care," Grinsted said of the other females.
Genetics and environmental differences help to forge such personalities.
Pruitt, of the University of Pittsburgh, further suggested that personalities are more pronounced in social species, perhaps explaining why individuals among humans, dolphins, dogs, cats, parrots and other social animals behave in very distinctive ways.
"Recent laboratory studies suggest that persistent social interactions are enough to create stable difference in individuals' personalities," he said. "That is, spiders that interact with the same individuals for long periods of time tend to form stable personalities. In contrast, spiders that interact with new individuals all of the time exhibit more flexible, variable personalities, so sociality itself may help to create variation in personalities."
Hormones, which can be affected by both genetic and environmental influences, are yet another likely factor.
Testosterone levels in humans can sometimes predict how aggressive the person is. In spiders, the key hormones appear to be octopamine and serotonin, which are being studied now. Macho male spiders and tough females could be pumped up on various hormones.
Deborah Gordon, a professor in the Department of Biology at Stanford University, told Discovery News that she agrees with the new study's conclusions. She indicated that measures of "boldness" could only just scratch the surface of a spider's unique character.
"Aggression is only one feature of differences among individuals," Gordon said. "There are many others we could look at."