Israel, one of the most densely populated countries on Earth, turns out to have been harboring an unknown species of butterfly. Nor was the insect lurking in some dank hole: it was discovered flying about Israel's only ski resort, Mount Hermon, by an entomologist and evolutionary biologist named Vladimir Lukhtanov from the Zoological Institute in St. Petersburg, Russia.

Lukhtanov says he was surprised that nobody ever realized this high-altitude fritillary (Melitaea acentria) was unknown to science.

"Thousands of people had observed and many had even photographed this beautifully colored butterfly, yet no one recognized it as a separate species," he said.

That is because most people don't spend their time peering at lepidopteran genitalia and thought the thing belonged to the common species called Persian fritillary, which looks, well, the same.

But as Lukhtanov describes in Comparative Cytogenetics, he and his students did that very thing in 2012, while carrying out a broad study of Israeli butterflies, and noticed something odd.

The genitals of the male Hermon fritillaries were unlike those of Persian fritillaries, though otherwise the butterfly species are phenotypically similar.

They then sequenced the butterflies and Lukhtanov, with his student Asya Novikova, discovered that the Hermon variant to be an unknown species. It also exists in Syria and Lebanon.

"The species is probably one of a handful of butterflies known to have arisen through hybridization between two other species in the past," says Lukhtanov. "This process is known to be common in plants, but scientists have only recently realized it might also be present in butterflies."

If so, the hybridization was not recent. A DNA barcode-based phylogeographic study showed the population to be ancient, possibly around 1.6 million years, say the scientists.

This is the first new butterfly species discovered and described from the territory of Israel in 109 years. Previously unknown plant species have also been found, such as a variant species of Colchicum flowers in the Negev. Much like the butterfly on the Hermon, it took a fine eye to notice the difference between it and other Colchicums, and again, the difference lay in the sex organs.