Invertebrates such as spiders and centipedes are underappreciated kings of the jungle, eating a surprising amount of vertebrates in the Amazon, a new study says.
Biologists recently documented 15 interactions in which the invertebrates are hunters and the vertebrates are prey. They captured photo and video evidence of invertebrates eating tadpoles, lizards, snakes—and even an opossum, a first-of-its-kind observation. (Read about tiny spiders that devour lizards three times their size.)
Though such behaviors have been recorded before, the study provides more data about just how many vertebrates fall victim to small predators, particularly spiders.
“Invertebrates preying on vertebrates is common, but it’s generally not assumed to be an important source of mortality for amphibians and reptiles,” says study leader Rudolf von May, a biologist at the University of Michigan.
“Our knowledge of these interactions remains limited.”
A novel discovery
Von May and colleagues made most of their observations at night in Peru’s lowland tropical rainforests, one of the most diverse ecosystems on Earth. Under the cover of darkness, the forest teems with eight-legged hunters, especially ctenids, commonly known as wandering spiders. (See photos of spiders that kill other spiders.)
“What stands out at night is the amount of spiders you see on all sorts of substrates—on the ground, on leaves, on branches,” says von May, whose paper appeared today in the journal Amphibian & Reptile Conservation. “When we do surveys at night, some of the spiders we see will have prey, typically other invertebrates like crickets and moths.”
“But once in a while, we see a spider with a frog or lizard.” (Read about fish-eating spiders.)
The team also collected the bodies of two snakes that succumbed to centipedes, including a venomous coral snake.
But one night survey revealed a sight none of the researchers had seen before: A tarantula the size of a dinner plate preying upon a small mouse opossum.
"The opossum had already been grasped by the tarantula and was still struggling weakly at that point, but after about 30 seconds it stopped kicking,” co-author Michael Grundler, a Ph.D. student says in a statement.
"We were pretty ecstatic and shocked, and we couldn't really believe what we were seeing," Grundler says.
Later, Robert Voss, a mammologist at the American Museum of Natural History, confirmed they had captured the first documentation of a large mygalomorph spider—commonly known as a tarantula—hunting and eating an opossum.
Rick West, an independent arachnologist and tarantula expert not involved with the study, notes by email that "tarantula predation on vertebrates is not a common thing, but it does happen. They are opportunistic feeders and they’ll take whatever they can subdue."
"In the South American rainforest, I’ve found that some of the larger tarantulas prey often on frogs, and that was reflected in this article."
Sleeping with the enemy
In addition to predation, the researchers confirm an earlier report of a special relationship between a certain frog and spider species. While the tarantula in the genus Pamphobeteus will usually jump at the chance to eat a frog, it allows individuals of one species, the dotted humming frog (Chiasmocleis royi), to share its underground burrow.
“We don’t know what’s preventing the spider from preying upon that frog,” says von May. “There are so many species of frog in the Amazon, and this is the only one we know of that is able to coexist with this spider.” (Read about a new Amazon frog named for a mythical monster.)
Von May and his colleagues speculate that the frog might provide some benefit to the spider, such as cleaning it of parasites.
“It may seem like everything is killing each other, but at least there is this one case in which frogs have figured out how to live with a spider.”
A forest full of critters
Considering this diversity and the sheer number of invertebrates in the Amazon, the potential for interactions between species is staggering.
“Natural history data such as these,” says von May, “are valuable for understanding how biological communities are organized in tropical rainforests.”