Jumping spiders, a spider family found worldwide, have four pairs of eyes and, as the name implies, a penchant for acrobatic jumping. These spiders don’t usually create webs to entrap their prey; instead, they utilize their silk as a “dragline” to help them improve their leaps or develop silken houses for mating, producing eggs sleeping safely at night, hidden away from predators.
Researchers discovered that a population of European jumping spiders repose at night by hanging on a lone strand of silk, similar to a bit of bungee cord, according to a study published in the journal Frontiers in Zoology.
The scientists speculate that in the dark, when their exceptional eyes aren’t of much help, these spiders may have another trick up their sleeve to get through the night securely, depending on these preliminary findings and earlier anecdotal reports from researchers on other continents.
Daniela Rößler, a Harvard University behavioral ecologist, started this study by chance. In Frankfurt, Germany, she collected numerous European jumping spiders and placed them in transparent boxes on her windowsill while working on a separate project. “I glanced at the spiders immediately and was like, ‘Oh goodness, did they die?'” she recounts after returning home one night. ‘What went wrong?’ All of them were dangling from the inside lid of the plastic box.”
Rößler and her coauthors went back to the grassland near Trier, Germany, where the spiders were first collected to discover more. They set up 12 two-square-meter plots and visited them twice a day (during the day and at night) over nine days, in addition to viewing some spiders in captivity. They collected measurements, examined how the spiders constructed this “suspension line,” and saw how they reacted to various interruptions while they were there.
She explains, “We discovered that they all hung.” “Even one day after emerging from the egg sac, the newborns can already do this behavior.” The spiders will anchor when they pick a place, which may be a patch of tall grass or plants, according to Rößler. “It’s really like a little 3D printer; they utilize their silk to manufacture little attachment discs.” They then drop a rope of silk and hang a few centimeters down, folding all of their legs but one to grab onto the thread. According to the researchers, the spiders were often still eating food when they settled down for the night.
According to Rößler, the spiders in captivity would alternate between their usual silken “retreats” and the hanging activity. “So, how do they pick what to use?” you might wonder. “What is the point of this?” says the narrator.
To begin deciphering the function, the researchers experimented with various perturbations, including flashing them with light, stroking adjacent flora, and physically stroking the silk. Almost all of the spiders in the latter test fell to the ground. The scientists suggest that the suspension may protect the spiders from predators at night, either by keeping them out of harm’s way or by allowing the momentarily blind spiders to identify possible predators through vibrations.
She explains, “They discern between all of these various disturbances.”
“When it was highly windy, they’d simply dangle in the air, but they didn’t seem to mind, indicating that they can differentiate between various vibration cues.”
Ana Cerveira, a behavioral ecologist from the Universidade de Aveiro in Portugal who was not involved in the study, stated to Popular Science, “I found the research issue pretty fascinating.”
“This discovery will undoubtedly affect future jumping spider research by calling attention to a behavior that may be more frequent than we thought in this family but is difficult to identify in both wild and laboratory conditions.”
According to Rößler, the study raised more issues than it addressed.
“It made me realise how little we know about animals in our backyards, particularly invertebrates.”