Epomis beetle larvae look great for frogs. They are snack sized, like small protein packs. When a frog is nearby, a larva will even wiggle its antennae and mandibles hesitantly.
But when the frog makes its move, the cage turns the tables. It jumps on the head of the amphibian and bites down. Then it drinks out its predator flux like a froggy Capri Sun.
We just think of food chains moving in one direction: Bigger food smaller. But nature is often not so beautiful. Around the world, and maybe even in your backyard, arthropods attract vertebrates and gag them up.
Jose Valdez, early postdoctoral researcher at the German Center for Integrative Biodiversity Research, identified hundreds of examples of this phenomenon in the scientific literature, which he detailed in a review published in July in Global Ecology and Biogeography. He and others studying the subject think that once the first whip of shock is over, it is important to understand what is eating.
Dr. Valdez became interested in these role changes during his doctoral research, after seeing a bunch of water beetles pollute a rare predator. The larvae were known predators, while the adults are widely regarded as scavengers. Mar Dr. Valdez developed a slug, elaborated by further research, that they are also actively hunting for wolves.
He got a similar feeling when, while reading the news or surfing YouTube, he saw other bugs sticking above their weight: a hunter-gatherer enjoying a pygmy posum, a praying mantis chewing a gecko’s face.
“Maybe this is not so rare,” recalls Dr. Valdez thinks.
Dr. Valdez found 1,300 similar examples, which he collected in a searchable database. The entries cover 89 countries and include many types of arthropod predator: preserved warblers such as scorpions and spiders, along with less well-documented cases such as dragonflies and sentipedes.
It’s a formidable catalog of revenge invertebrates: A spider snorts a songbird in its web, giant waterbugs wrestle snakes in submission, fireflies team up to transmit a baby alligator. “Every time I read a new one, I was, ‘Oh my goodness,'” said Dr. Valdez.
There are a few complete studies on the subject; Dr. Valdez built on the work of Martin Nyffeler, a conservation biologist at the University of Basel in Switzerland who has documented spiders that eat everything from fish to bats. Another major contribution came from a 1982 literature review by Sharon McCormick and Gary Polis. Many of the matchups that Dr. Valdez added to his database were originally described in brief observatory notes by scientists who did not intend to study the subject.
After witnessing the smuggling of water beetle predators, Dr. Valdez also wrote it down as a note. But treating these specimens as one-offs could have hidden a greater ecological significance, he said, “We need to see what kind of effect this has on food webs.”
It could also have consequences for conservation, Dr Valdez said. He points to the case of the Devils Hole pupfish. Scientists struggled to breed the rare species in a laboratory to save them until they realized that diving beetles – accidentally imported from the pupfish’s habitat – ate many of the larvae.
It’s difficult to research what arthropods eat, said Eric Nordberg, a wildlife ecologist at James Cook University in Queensland who also studied the subject but was not involved in the new paper. If you want to learn more about what a vertebrate eats, “you can flush the contents of the stomach or look at preserved specimens,” he said. But invertebrates lack stomachs, so “you need to be in the right place at the right moment.”
These moments of serendipity are becoming more frequent, said Gil Wizen, one of the entomologists who discovered the unique behavior of the Epomis beetles. He argued the prevalence of smartphones, as scientists and the public were “more alert to these interactions,” he said.
Even with the new database, however, he did not think scientists had seen it all. “Without a doubt, there are more arthropods hunting vertebrates,” he said. “Nature is more fluid than we think.”
