When we think of spiders, we often envisage webs but silk-spinning arachnids use this super-strong substance in all kinds of ways. From the nets sprung on prey by the ogre-face spider (which can hear via its legs) to the lassos thrown by bolas spiders, spidey silk comes in all shapes and sizes. Now, new research has discovered another surprising way in which a spider uses silk, as a species in Madagascar was observed sewing leaves together to create what seemed to be a trap for prey, particularly one unlucky frog.
The unusual sighting, described in the journal Ecology and Evolution, was an incidental finding made by a team of researchers who were carrying out ecological surveys in Madagascar. One morning, after completing a bird point count in Ambodiala, they spotted a spider (Sparassidae, Damastes sp.) feeding on an amphibian. Invertebrates feeding on vertebrates is not unheard of, as demonstrated in the unfortunate fate of a pygmy possum, but the researchers believe their report to be one of just two describing such a predation event in Madagascar.
The same spider species was spotted on three other occasions, mostly in vanilla plantations across the region. What was most fascinating of all was that the spiders were all spotted either close to or inside a leafy retreat that had been sewn together with silk. The retreats were partially open presenting what appeared to be a cool hideaway for hot frogs caught in the Madagascan sun but little did they know inside a spider was waiting to pounce.
The first spider that was found eating a frog was reported to retreat back into its leafy hideaway when the researchers approached to take a picture. The other spiders were either close to or still inside similar leafy retreats and the spiders didn’t appear to have a preference for tree species as the leaves of different trees were used to craft the retreats. What connected them however was that they all showed evidence of being sewn together with spider silk.
“When temperatures rise, the frogs look for shade and cover away from the ground, which the spiders provide in form of their retreat,” wrote the authors in the paper. “The frogs might favor the seemingly protected traps in an attempt to hide from other predators such as birds that scan the vegetation for prey… We speculate that amphibians may not only be an opportunistic, indiscriminate, or accidental prey, but rather a targeted systematically exploited food source of Damastes sp. spiders."
The researchers recognize limitations in the study as only a single observation was made of a spider feeding on a frog. They also recognize that large prey items such as a frog are more easily spotted by the human eye and shouldn't be considered as evidence that it's a common behavior. However rare, that the silk spinners have added embroidery to their skillset is unquestionably awesome.