What spiders eating weird stuff tell us about complex Amazon food webs

Rare views of invertebrates munching on vertebrates include a tarantula and an opossum

WHAT’S FOR DINNER? Documenting invertebrates of the Amazon rainforest chowing down on vertebrates, such as this fishing spider with a tadpole in its mouth, helps scientists connect the dots of the Amazon’s intricate food web.

Emanuele Biggi/Amphibian & Reptile Conservation 2019

By Jeremy Rehm

February 28, 2019 at 12:09 pm

Rudolf von May has seen some pretty wild things in Peru’s Amazon rainforest. But this took things to a whole new level. There, caught on a team member’s cell phone video, was a giant tarantula, about the size of a dinner plate, weeble-wobbling through the leaf litter with the body of what was later identified as a mouse opossum hanging from its fangs.

“It was very surprising, to some extent shocking,” says von May, an ecologist at the University of Michigan in Ann Arbor, of the first-ever recording of such an encounter. “It’s very rare to see mammals being preyed upon by a large spider.”

Along with his colleagues, von May has made regular three- to four-week trips to the rainforest for at least the past 10 years. Each night, the team divides into groups and hikes through thick humidity and clouds of biting insects to collect data on amphibians and reptiles — from counting critters to taking tissue samples.

And, it turns out, they’ve also discovered some surprising insights into who’s eating who. From 2008 to 2017, the team documented 15 instances of invertebrates preying on vertebrates. These encounters included everything from a wandering spider gripping a Bolivian bleating frog, to a centipede eating an extremely poisonous juvenile coral snake that it had decapitated. And, of course, there was the jaw-dropping tarantula vs. opossum. The findings were published February 28 in Amphibian & Reptile Conservation.

SHOCKING SCENE When researchers working in the Peruvian Amazon rainforest heard scrabbling in the leaf litter, they shined their flashlights on the ground and witnessed something never documented before: a dinner plate–sized tarantula (Pamphobeteus sp.) dragging a young mouse opossum (Marmosops noctivagus) it had killed.

“It is very valuable and necessary to document these interactions in the field because tropical ecosystems are super diverse,” von May says. That biodiversity makes it difficult to know exactly how organisms affect one another. Scientists have known since at least the 1980s that invertebrates, which frequently have vibration-detecting hairs or paralyzing venom, play a crucial role in the consumption of vertebrates.

But how frequent and diverse such interactions are remains uncertain. “We just have very limited knowledge,” von May says. Now, at least, there’s more proof of how broad — and complex — the Amazon food web gets.