Japanese scientists have found that radiation from Japan’s Fukushima nuclear disaster has mutated a domestic butterfly species. It may not have morphed into Mothra, but the pale glass blue butterfly has displayed genetic and physiological changes.

The biological effects of Fukushima are just now being realized. A radioactive tuna caught international headlines in May, and at the same time, scientists from the University of Ryukyus were quietly monitoring mutations among samples of butterflies.

A paper was published in the journal Nature last Thursday detailing the findings. The study was conducted by academics who declared no competing financial interest, which means there are no red flags about any sponsor’s involvement with the research.

“Although epigenetic effects cannot be entirely excluded, it is most likely that the abnormal phenotypes observed are produced by random mutations caused by the exposure to radiation,” the report says. Mutations affected the insects’ appendages, which were frequently malformed.

Other abnormalities were observed in antennae, palpi, eyes, abdomen, and wings; an uncommon wing spot patterns was also noticed in many of the samples. The authors concluded that their findings were consistent with previous field studies near Chernobyl, and concluded that the butterfly was the “best indicator species for radionuclide contamination in Japan.”

Aerial contamination was widespread, but the Pacific Ocean bore the brunt of it. During the Fukushima disaster, levels of radioactive cesium peaked at 50 million times normal levels, becoming the largest accidental release of radiation into the ocean in history. Strontium, which has an even longer half-life, also leaked out.

“Our demonstration of heritable germ-line genetic damage caused by low-dose exposure due to radioactive contamination in a species of butterfly has invaluable implications for the possible future effects of radiation on animals,” the study concluded.

It also suggested that more investigations on Fukushima’s biological aftermath are warranted. Elevated levels of radiation have been found in Japanese school children that live in communities near the Fukushima site, rice crops, and even cattle.