In the afternoon in the hot weather in northeastern Madagascar, the frogs search for shady places to protect themselves from the evil of drought caused by the high temperature, and the coldness of the shade of a leaf may be the right place for an attractive rest period.

But some of these cold oases may be a trap, as these paintings may hide a handful of hungry skilled architects, like the Sparassidae, a species that follows the order of modern spiders, which sew plant leaves using silk threads to create cool and tempting mock shelters to lure the frogs to their doom. .

And researchers reported - in a study published on December 11 in the journal Ecology and Evolution - that one of these hunting spiders was seen eating a frog inside one of these paper pockets.

Their new observations showed that spiders partially tie two sheets together using silk, suggesting that the spiders deliberately weave these unique structures to attract and lock the frogs.

Prey on vertebrates

Some spiders are known to prey on larger and more powerful vertebrates such as opossums and even frogs, if given the chance, and when that happens, spiders are usually seen as having won the jackpot.

But researchers say that hunting spiders, in turn, may specifically target frogs as prey, and by binding the leaves together, the spiders create delicate, cool, dark habitats that are desirable in a dry and scorching environment for many creatures.

Spiders are the most invertebrate groups that prey on vertebrates, however, few reports have been published that talked about events of amphibian predation by invertebrates, and the researchers in this new study present the second report on spider predation of vertebrates from Madagascar, East Africa.

The hunter spider hides in a pocket of tree leaves and spider silk, waiting for its prey (Ecology & Evolution)

Researchers have reported one case of predation of the Damastes spider, a genus of hunting spiders that ate a small frog, and that happened in 2017 and 2018, when Theo Rosen Fulgens, a biologist from the University of Antananarivo in Madagascar and his colleagues, conducted an environmental survey after Dominic Martin discovered, from University of Göttingen, Germany, a large hunter spider eating a small frog in Madagascar.

The spider was on a small tree, near a pair of overlapping leaves that had been tied with spider silk to create a pocket, and the spider appeared in its lush lair, pulling the frog to feed on it.

In the new study, researchers observed 3 individuals of the same spider species sitting in cells made of green leaves attached to the tree trunk.

Two sheets of spider silk were woven into the top, and the edges at the base of the leaves seemed to enable the prey to climb the tree trunk to enter.

"The first time we discovered this phenomenon, we were very excited," says Folgens.

The following year, while conducting surveys of reptiles and amphibians in roughly the same area, we found 3 other spiders hiding in similar leaf shelters, but these spiders were not detected with prey.

Trapper spider feeding on a frog in Madagascar inside a pocket of tree leaves (Ecology and Evolution)

Intense controversy

This study sparked a lot of unprecedented scientific controversy, and Stano Picard, a behavioral biologist at Masaryk University in Brno, Czech Republic, who was not involved in the research, told Science News website: “These spiders can simply hide. The ambushes are placed on passing prey, and the leafy structures are not used as traps. "

José Valdez, a conservation biologist at the German Center for Integrative Biodiversity Research in Leipzig, who was not involved in the study, agrees. “What makes me think otherwise is that the researchers didn't just discover it several times, but the spider was weaving the edges of the leaves,” he says.

Part of the reason for the uncertainty is that a spider that was spotted eating a frog was first seen outside the leaf pocket where the spider was devouring its prey.

"Only detailed observations and experiments can confirm whether the leaves trap frogs," says Rodrigo Willemart, a zoologist at the University of Sao Paulo, who was also not involved in the research.

If so, it could be a unique tool among spiders. "I don't know of any of the research papers that talked about traps that spiders built specifically to capture vertebrates," says Willemart.