Spiders’ weird meals show how topsy-turvy Amazon food webs can be

Rudolf von May has seen some pretty wild things in Peru’s Amazon rainforest. But a team member’s cell phone video took things to a whole new level. It showed a giant tarantula about the size of a dinner plate. Even more surprising? The spider wobbled through the leaf litter with the body of a mouse opossum hanging from its fangs.

An ecologist, von May works at the University of Michigan in Ann Arbor. To see the first-ever recording of such an encounter “was very surprising — to some extent shocking,” he says. “It’s very rare to see mammals being preyed upon by a large spider.” Far more common is to see predators that are vertebrates higher up the food chain.

Over the past 10 years, von May and his colleagues have made many trips to the rainforest. Each may last three to four weeks. At night, the team divides into groups and begins hiking. They trek through thick humidity and clouds of biting bugs in search of data on amphibians and reptiles. Depending on the project, they might count critters or take tissue samples.

Along the way, they’ve discovered some surprises about who’s eating who. From 2008 to 2017, the team logged 15 instances of invertebrates — animals without a backbone — preying on vertebrates. Once, it was a wandering spider gripping a Bolivian bleating frog. Another time, a centipede nibbled on a very venomous young coral snake — that it had beheaded. And, of course, there was the jaw-dropping tarantula vs. opossum. The researchers described these strange meals February 28 in Amphibian & Reptile Conservation.

“It is very valuable and necessary to document these interactions in the field because tropical ecosystems are super diverse,” von May says. With so many organisms around, it’s hard to know how they all interact.

Many invertebrates are predators. Some have vibration-detecting hairs or paralyzing venom to help catch prey. And scientists have known since at least the 1980s that spineless critters can eat vertebrates.

But it’s not known how common such events are. “We just have very limited knowledge,” von May says. Now, here’s more proof of how complex — and topsy-turvy — the Amazon food web can be.