Scientists found unusually small wings and mutations in the legs and antennae of insects collected May last year, two months after the earthquake and subsequent tsunami struck.
The radiation exposure harmed their genes and the damage could be passed on to future generations, the 'Daily Mail' reported.
"Artificial radionuclides from the Fukushima (No 1) nuclear power plant caused physiological and genetic damage" to pale grass blue butterflies, a common species in Japan, according to the Journal 'Scientific'.
"Sensitivity (to irradiation) varies between species, so research should be conducted on other animals," said Joji Otaki, a team member and associate professor at the University of the Ryukyus in Okinawa.
Researchers collected 121 adult pale grass blue butterflies in and outside Fukushima Prefecture in May 2011, two months after the nuclear crisis started after a 7.1 magnitude earthquake followed by a powerful tsunami.
Abnormalities such as unusually small wings were found in 12 per cent of the total.
The rate rose to 18 per cent in a second generation produced through mating among the butterflies collected and some even died before reaching adulthood.
When second generation butterflies with abnormal traits mated with healthy ones, the rate of abnormalities rose to 34 percent in the third generation, according to the article.
However, it nearly doubled to 52 per cent among a second generation born to the original butterflies caught.
Scientists said the butterflies collected in May were heavily exposed to radiation as larvae.
The impact of artificial radiation exposure on the species was also investigated using larvae collected in Okinawa, one of the prefectures least affected by fallout from the nuclear disaster.
