“They take a few steps and then they stop and vibrate their abdomen, and then they take a few steps and vibrate again,” study researcher Samantha Vibert, a doctoral candidate at Simon Fraser University in Canada, said of the males.
Vibert and her colleagues reported their findings in the journal Frontiers in Zoology.
Spiders use their webs as extensions of their bodies, able to sense vibrations on the threads that trigger their response to prey. But when an arachnid gentleman caller comes along, he runs the risk of being mistaken for a delicious moth and attacked.
Vibert knew from observing hobo spiders that mating spiders perform elaborate dances. She wanted to know what was behind these complex displays.
To find out, she and her colleagues investigated two web-dwelling spiders, the western black widow and the hobo spider. Hobo spiders produce sheet webs, whose familiar, organized patterns usually come to mind when people think of spider webs. Black widows produce tangle webs, which look like cobwebs.
First, the researchers recorded vibrations of male spiders venturing onto females’ webs as well as the vibrations made when a house fly or house cricket got trapped by the sticky silk. The researchers then compared the vibrations’ duration, frequency and amplitude. They found that prey and potential mates make very different vibrations. The male spiders produced continuous, long-duration vibrations with low amplitudes, meaning that they were “quiet” compared with the sporadic, percussive vibrations made by trapped prey.
The differences were especially pronounced in black widow spiders, Vibert said. Male black widows produced these good vibes by moving their abdomens in a rapid motion — reminiscent of twerking.
Next, the researchers played recorded vibrations onto webs occupied by females. The scientists tested vibrations from both prey and male spiders, played on either high or low, and watched how the females responded.
“It didn’t really matter what the vibration sounded like, but it had to be quiet,” Vibert said. “If you play back a very quiet, whisperlike vibration, then the females did not respond aggressively.”
Strong vibrations sent the female spiders scurrying over in attack mode. But little whispers simply got their attention — some turned toward the source of the vibrations, and some even responded with abdominal twitches of their own, suggesting back-and-forth communication.
“I think what really blew my mind was just how complex their signaling system is,” Vibert said. Courting spiders often show off with graceful dances, bobbing, weaving and circling around their intended mate, Vibert said.
“Spiders can be really beautiful, and they’re a lot more complex than most people give them credit for,” she said.
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