Pitcher plants are even more carnivorous than we imagined, regularly feasting on salamanders, a new study shows for the first time.
Vertebrates, ranging from frogs to rats, have been seen in the sticky jaws of pitcher plants before, but were “thought to be a rare prey trapped accidentally,” says Kazuki Tagawa, an ecologist from Tottori College in Kurayoshi, Japan, who wasn’t involved in the research.
Study leader Patrick Moldowan, an ecologist at the University of Toronto in Ontario, Canada, was making his rounds of a bog in Algonquin Provincial Park in August 2018 when he spotted the bizarre behavior. (Read more about carnivorous plants and their fatal attraction.)
“The very first plant that I kneeled down and peered into had captured a salamander, and it was alive and swimming,” he says.
Interest piqued, he and his colleagues spent the next month and a half peeking into the contents of northern pitcher plants (Sarracenia purpurea). The team observed juvenile spotted salamanders in almost 20 percent of plants surveyed; many traps contained more than one, with a total count of 35 individuals.
The scientists believe the amphibians provide a big boost of nutrients in food-scarce, highly acidic bogs, where carnivorous plants have evolved to live. The newly recorded behavior may also be a concern for spotted salamander populations, which already occur in low densities throughout Ontario’s bogs.
Pitcher plants typically use nectar to attract prey such as pollinating insects, which fall into a tiny pool of water at the plant’s base, where they’re slowly digested. (Learn about a meat-eating plant that steals bugs from its neighbors.)
It’s possible the salamanders ended up in the pools while seeking refuge, or they were drawn to insects attracted by the plant. “In turn, with one wrong slip, they themselves could become the meal,” says Moldowan.
In any case, he says it’s strange that the behavior wasn’t noticed before, since these pitcher plants and salamanders are both common species.
That may be because previous studies have typically examined the plants’ contents in spring and summer, while the salamanders seem to fall victim to the plants in late summer and early fall—the period during which they metamorphosize and are transitioning from an aquatic to terrestrial habitat.
There’s likely a seasonal component to the pitcher plants’ predation, too: Cold can settle in as early as September, and such large prey would be a huge benefit when insects become scarce in winter. (Read about the world’s largest carnivorous plant.)
“Compared to any sort of invertebrate life that these plants might capture, salamanders offer hundreds to thousands of times more in nutrient inputs—things like nitrogen and phosphorus,” says Moldowan.
Catching salamanders could have a downside for the plants, though: Large prey can rot in a trap before it is fully digested, potentially killing the plant.
Tagawa is interested in how efficiently a pitcher plant can digest a salamander following its capture, which hasn’t yet been investigated. According to the new study, it took between three and 19 days for salamanders to die inside the plant. They may be literally cooked to death when the small pool of water heats up in the sun, says Moldowan.
Expanding the menu
The findings could have repercussions for spotted salamander populations on top of water pollution and habitat loss, the authors say. So far, however, the amphibian’s numbers do not seem to be declining, and the International Union for Conservation of Nature lists the species as of least concern.
Going forward, Moldowan plans to research “whether these big pulses of nutrients benefit the plant in growth in the next year.”
He also wants to find out if pitcher plants frequently tuck into other vertebrates; he didn’t find frogs or toads in his recent survey, possibly because it was the wrong time of year.
“This year, I'll more specifically try to address that by sampling over a wider period of time,” says Moldowan.
“This is probably a much more widespread phenomenon than we currently recognize.”