The first creatures definitively shown to have mutated following the Fukushima meltdown are pale blue grass butterflies, but it's still a long way from proving human mutation, scientists said. Somehow, that's not all that comforting.

The study proving the mutations, published in the Nature sibling publication Scientific Reports, showed that the butterflies, which its authors, Atsuki Hiyama, Chiyo Nohara, Seira Kinjo, Wataru Taira, Shinichi Gima, Akira Tanahara, and Joji M. Otaki called "the best indicator species for radionuclide contamination in Japan," had their mutation rate increased as they bred after being exposed to the radiation leaked by a meltdown at Fukushima caused by an earthquake and tsunami in March 2011. "Some of the butterflies had abnormalities in their legs, antennae, and abdomens, and dents in their eyes," CNN reported. "Researchers also found that some affected butterflies had broken or wrinkled wings, changes in wing size, color pattern changes, and spots disappearing or increasing on the butterflies."

One of the researchers on the study, Joji Otaki, told The Japan Times that "humans are totally different from butterflies and they should be far more resistant," and the study itself includes a line explaining that "the effects of low-dose radiation exposure on animals, including humans, are still a matter of debate." But as Gizmodo's Mario Aguilar points out, the much more alarming language comes just prior to that pacifying sentence, as scientists make connections to other radioactive disasters and their links between animal and human mutations:

In the case of the Chernobyl accident, changes in species composition and phenotypic aberration in animal sand an increase in the incidence of thyroid and lymph cancers in humans have been reported. Similarly, an increase in the incidence of cancers has been reported for atomic bomb survivors in Hiroshima and Nagasaki, Japan.

So, yeah, radioactive mutations are in play in the Fukushima fallout, and while they're affecting butterflies now, that doesn't necessarily mean they'll stay relegated to the insect world. Scary.