Thirty years ago, the large blue butterfly (Maculinea arion) disappeared from England, the victim of over-eager collectors and habitat degradation. But today the species is thriving in the UK, and boasts more colonies than before its populations started declining in the 1950s.

What made the restoration of the large blue butterfly a success? Much of the credit goes to Jeremy Thomas of the University of Oxford and the Centre for Ecology and Hydrology in Wallingford.

Before the large blue vanished, Thomas spent years studying their last remaining colony in the UK. "From May to late September, I was living with the last UK colony, measuring everything, including their behavior, how many eggs they laid, the survival of individual eggs, how many caterpillars were in the plants. It was a bit like a detective story," Thomas said in a statement.

What he discovered laid the groundwork for the successful reintroduction of the species. The story will finally be told this week in the journal Science, and it may offer lessons to help save other at-risk species.

It turns out that, like many butterflies, the large blue tricks local ants into rearing its young caterpillars. But unlike other species, the large blue relies upon a specific red ant, Myrmica sabuletiI, for its nanny services. Because of that unique relationship, the butterfly's population started to crash when that ant species declined.

The ants ran into trouble when farmers stopped grazing their livestock as they had for generations and a virus ravaged the population of wild rabbits. Grasses grew too long, causing soil temperatures to drop by a few degrees. That was just cold enough to make the area inhospitable to the ants, and that hurt the butterflies.  “If you're the size of an ant or butterfly that difference is massive," Thomas said.

With this information in hand, Thomas and his colleagues began restoring the large blue's habitat to ideal conditions. Once a few habitats were ready, the reintroduction of butterflies from Sweden began.

It was Thomas's focus on young and juvenile butterflies that made the difference, and his research shows that ecologists can save time and find more clues to saving troubled species by examining the life patterns of their young than a species' entire life cycle.

It's too early to say how much impact this research and its conclusions will have, but with many other locally extinct species -- such as the beaver and red kite -- being reintroduced to the UK, the story of the large blue may soon have a sequel.

Image: Maculinea arion, David Simcox, Centre for Ecology and Hydrology, UK. Used with permission.