This story originally appeared in The Bulletin of the Atomic Scientists and is part of the Climate Desk collaboration.

When a massive earthquake followed by a tsunami hit Japan a decade ago, the Fukushima Daiichi Nuclear Power Plant experienced a catastrophic meltdown. Humans fled a wide area around the plant that today is known as the Fukushima Exclusion Zone, while animals and plants remained. Now, scientists have enlisted the help of snakes in the zone to make sense of the disaster’s impact on the environment. Their findings, reported in an Ichthyology and Herpetology paper, indicate that Fukushima’s native rat snakes, like canaries in a coal mine, may act as living monitors of radiation levels in the region.

“Because snakes don’t move that much, and they spend their time in one particular local area, the level of radiation and contaminants in the environment is reflected by the level of contaminants in the snake itself,” Hannah Gerke, a lead author on the study, said.

Animals, plants, or other life forms whose health provides insight into environmental health are known as bioindicators. For example, frogs, with their permeable skin and limited abilities to detoxify, are bioindicators of environmental pollution. And lichens, which have no roots and rely on nutrients from the atmosphere, are bioindicators of atmospheric pollution. Gerke’s recent study suggests that rat snakes may be useful bioindicators of radioactive contamination in nuclear disaster zones. But that does not necessarily mean that Fukushima’s environment or its snakes are languishing.

“Everybody expects Fukushima to be a barren wasteland full of mutated animals. In real life, it is quite beautiful,” Gerke said. “I was there in summer when everything was lush and green. There is wildlife everywhere—just a surprising lack of people.”

The scientists’ findings reinforced their 2020 study that found a high correlation between levels of radiocesium—a radioactive isotope of cesium—in the snakes and levels of radiation in their environment.

Why snakes and not, for example, birds? Not every animal in Fukushima’s exclusion zone is suited to the “work” of a bioindicator. That’s because the radiocesium that spewed from the nuclear disaster did not blanket the region evenly. For example, birds that travel far are exposed to contaminants all over the zone, which leaves them unable to provide insight into degrees of contamination in the zone’s smaller “neighborhoods.” But rat snakes have relatively small home ranges; they travel an average of 65 meters (approximately 213 feet) each day, according to the study. And they are susceptible to accumulating radionuclides—unstable atoms with excess nuclear energy—from disasters such as the one that took place in Fukushima. A rat snake that makes its home in a small but heavily contaminated area will tell a different story than a rat snake that lives in a less contaminated locale.

In the decade since the nuclear disaster, most of the contaminants have settled in the soil. This means that animals such as birds that spend much of their time in trees have limited insight to offer about contaminants on the ground. But snakes, whose long bodies slither in and burrow under the soil, can help determine degrees of contamination.

Also, snakes live long, which means that the data they gather provides information about environmental contaminants over time.

How did scientists enlist the help of the snakes? The rugged Abukuma Highlands are situated approximately 15 miles northwest of the Fukushima Daiichi Nuclear Power Plant. This verdant terrain of hills and valleys is peppered with abandoned villages and farms—and, for a few recent months, scientists in search of snakes.