It's no surprise that radiation is bad for animals, but how much is too much? Researchers in Japan decided to put this question to the test for the pale grass blue butterfly, a species commonly found around the remains of the Fukushima Daiichi Nuclear Power Plant. And, they discovered, even a small amount of radiation is too much.

Rather than study butterflies in the environment, the researchers performed meticulous lab experiments on specimens collected in Okinawa, far from any radioactive contamination. The scientists collected plant material from around Fukushima and fed it to pale grass blue butterfly caterpillars.

When the caterpillars turned into butterflies, they suffered from mutations and were more likely to die early than ones that had not eaten radioactive plants. This finding applied even to those butterflies had only eaten a small amount of artificial caesium as caterpillars. "We conclude that the risk of ingesting a polluted diet is realistic, at least for this butterfly, and likely for certain other organisms living in the polluted area," the team concludes.

In other words, things don't look good for the animals living around Fukushima.