Epomis beetle larvae look delicious for frogs. They are snacks, like small protein packs. If a frog is nearby, a caterpillar will even turn its antennae and mandibles enticing.
But when the frog moves, the beetle turns the tables. It jumps on the amphibious head and bites down. Then it drinks its predator fluids like a lush Capri Sun.
We tend to think of food chains moving in one direction: Bigger eat less. But nature is often not so beautiful. All over the world, and maybe even in your garden, arthropods relieve vertebrates and buzz them.
Dr. Valdez became interested in these role changes during his doctoral research, after seeing a bunch of water beetles devour a rare butt bowl. The larvae were known predators, while adults were generally considered to be raggers. But Dr. Valdez developed a sigh, based on further research, that they also actively hunted vertebrates.
He got a similar feeling when, while reading the news or browsing YouTube, he saw other bugs punching over their weight: a hunter-spider enjoying a pygmy possum, a mantis chewing away a gecko’s face.
“It may not be so rare,” Valdez remembered thinking.
Dr. Valdez found 1,300 similar examples, which he collected in a searchable database. The reports cover 89 countries and include many types of arthropod predators: storied backbone hunters such as scorpions and spiders, along with less well-documented cases such as dragonflies and millipedes.
It’s a formidable catalog of invertebrate revenge: A spider snares a songbird in its web, giant water sucks wrestling snakes into submission, fire ants work together to exceed a baby alligator. “Every time I read a new one, I was ‘Oh my goodness,'” Dr. Valdez said.
There are few full studies on the subject; Dr. Valdez is based 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 matches that Dr. Valdez added to his database was originally described in short observation notes by researchers who had not intended to study the subject.
After witnessing his banging of the water beetle, Dr. Valdez also wrote it as a note. But that he treats these instances as one-off characters could hide a greater ecological significance, he said: “We should see what kind of effect this has on food paths.”
It can also have consequences for conservation, said Dr. Valdez. He points to the case of the Devils Hole puppy fish. Researchers had trouble breeding the rare species in a lab to save them until they realized that beetles – accidentally imported from the puppy’s habitat – ate many of the larvae.
It is difficult to investigate what arthropods eat, said Eric Nordberg, an ecologist in wildlife at James Cook University in Queensland who has also studied the subject but has not been involved in the new thesis. If you want to learn more about what a vertebrate eats, “you can flush the stomach contents or look at preserved samples,” he said. But invertebrates have no stomach, so “you have to be in the right place at the right time.”
These moments of serendipity are becoming more common, said Gil Wizen, one of the entomologists who discovered the unique behavior of Epomis beetles. He credited the proliferation of smartphones, as well as the fact that researchers and the general public became “more alert to these interactions,” he said.
Even with the new database, however, he did not think that researchers had seen it all. “Without a doubt, there are more arthropods hunting vertebrates,” he said. “Nature is more fluid than we think.”