Pitcher plants—carnivorous flora that can be found across the world—have long been known to dine on living things, usually small insects and spiders. These plants have occasionally been spotted preying on larger vertebrates, but scientists believed these were rare occurrences. Canadian researchers were therefore quite surprised when they repeatedly observed pitcher plants snacking on baby salamanders.
In August 2018, Alex Smith, a biologist at the University of Guelph, was conducting field work with a team of undergraduates in Ontario’s Algonquin Park, a vast stretch of hills, forests and lakes. Smith peered into a pitcher plant, expecting to find some small insects decaying in the liquid that pools inside the plant’s pitcher-shaped leaves. Instead, “I see a juvenile yellow spotted salamander,” Smith tells CBC Radio. “And I say, ‘WTF?’”
Smith consulted with Patrick Moldowan, an ecologist at the University of Toronto who studies the salamander biology. Moldowan recalled that a 2017 survey had observed eight salamanders—six still living and two dead—inside pitcher plants living in a naturally acidic, fishless bog in Algonquin. Pitcher plants have evolved to thrive in such hostile environments. Bog soils are poor in nutrients like nitrogen, so pitcher plants use nectar to entice prey, which get caught in the plant’s liquid pool and are eventually broken down by digestive enzymes.
In August and September of 2018, Moldowan conducted a more extensive survey of the site and found that around 20 percent of the pitcher plants he looked at contained captured salamanders. In total, 35 individuals were spotted. Some plants had more than one salamander inside.
In their latest study in the journal Ecology, the researchers write that the “high frequency of salamander captures in pitcher plants suggests that salamanders might be a substantial nutrient source for pitcher plants.” This reason the phenomenon may have gone unnoticed previously could just come down to a matter of timing. According to National Geographic’s Sandrine Ceurstemont, previous studies have typically looked at pitcher plants in the spring and summer. The scientists behind the new report, by contrast, timed their survey to coincide with the period of metamorphosis when young salamanders transition from aquatic to terrestrial environments, which happens in late summer and early fall.
The study authors speculate that as the salamanders are emerging onto land, they make the unfortunate decision to use pitcher plants for refuge. “When plants were approached or disturbed, most salamanders rapidly swam to the bottom of the pitcher and tightly wedged themselves out of sight in the narrow, tapered stem of the pitcher,” the researchers note. But it is also possible that the amphibians are drawn to the unassuming predators by insects that flock to the plants to feed on their nectar. And in some cases, the salamanders might accidentally be falling inside the plant.
Once trapped, it took between three and 19 days for the salamanders to die, according to the study. A variety of factors may have killed the animals, including drowning, starvation, infections and even heat. Temperatures inside the pitcher fluid might “exceed the tolerable thermal maximum of trapped salamanders,” the researchers write.
According to Smith, the new study offers a reminder of the many secrets that could be hiding in even well-trodden parts of the natural world. “This crazy discovery of previously unknown carnivory of a plant upon a vertebrate happened in a relatively well studied area on relatively well studied plants and animals,” he writes in an email.
The discovery also raises a number of intriguing questions that the research team hopes to investigate in the future, like whether pitcher plants are a significant form of mortality for young salamanders, and whether salamanders constitute a significant nutritional source for the plants. “This study and survey,” Smith writes, “are only the beginning.”