Blue moon butterfly

The amazing story of eggfly from google sources for your read -

On the Samoan Islands of Upolu and Savai'i, a parasite (probably Wolbachia) had been killing the male members of Hypolimnas bolina. The problem was so severe that by 2001, males made up only 1% of the population. However, in 2007, it was reported that within a span of just 10 generations (about 5 years), the males had evolved to develop immunity to the parasite, and the male population increased to nearly 40%.

“We usually think of natural selection as acting slowly, over hundreds or thousands of years," said study team member Gregory Hurst, an evolutionary geneticist at the University College London. "But the example in this study happened in a blink of the eye, in terms of evolutionary time."
The scientists think the males developed genes that hold a male-killing microbial parasite, called Wolbachia, at bay.

The results, detailed in the July 13 issue of the journal Science, illustrate the power of positive natural selection on “suppressor” genes that thwart the lethal bacteria, allowing the male butterflies to bounce back.