Frogs have difficult lives in South American rainforests. Many of them are preyed by Snakes and by Artropods, especially by spiders which are big and particularly active at night. But there is a frog that developed a peculiar relationship with some spiders. This is the Microhylid Chiasmocleis ventrimaculata, who lives, often in good numbers, near spider burrows of some tarantulas species. The spider, a still undescribed Theraphosidae of the genus Pamphobeteus, tolerates the frog and never attacks it. Other amphibians passing outside his burrow are immediately captured, even by the young specimens which, in this species, remain with the mother for many month with no sign of cannibalism. This curious relationship is one of the few cases of mutualism between amphibian and spiders (the other involves Xenesthis immanis instead of Pamphobeteus sp.) for the first time photographed with such detail.
The advantages for the Chiasmocleis are obvious. She won't be attacked by other spiders and by small snakes: intrusions are not tolerated in the tarantula territory. And it’s possible the Arachnid is somehow helped by the frog who preys upon small parasites (mainly Diptera) and possible ants that could harm the spider or its eggs.

On Amphibians see also Saving frogs into the Amazon
On Arachnids see also Surprising spiders