In 1979, somewhere in Dartmoor, a butterfly died. That would hardly have been an exceptional event, but this individual was a Large Blue butterfly (Maculinea arion) and it was the last of its kind in the United Kingdom. Over more than a century, the Large Blue’s population had been declining and it was finally declared nationally extinct 30 years ago.
Now, it’s back. A bold conservation effort managed to work out the factors behind the butterfly’s decline, and resurrect this vanished species. The Large Blue’s reintroduction has been one of conservation’s flagship successes and it was the first time that efforts to save a declining butterfly had actually paid off.
The victory hinged on strong science. Rather than relying on speculation and optimistic measures, a team of scientists led by Jeremy Thomas, David Simcox and Ralph Clarke carefully analysed the factors behind the butterfly’s decline to find the best ways of reversing it. Work started in 1974 and the butterfly staged its comeback in 1983. Now, on the 25th anniversary of its reintroduction, Thomas, Simcox and Clarke describe their efforts to bring the charismatic Large Blue back to England’s green and pleasant lands.
The Large Blue butterfly has a very strange lifestyle. When it hatches in July, its caterpillar feeds on thyme plants for three weeks and then drops to the ground to begin a more leisurely existence. The caterpillar so strongly mimics the smells and sounds of the ant Myrmica sabuleti that it is carried to the colony and cared for as if it were an actual ant. It spends the next 10 months of its life in this sheltered environment, and its mimicry ensures that its surrogate parents leave it alone, even when it eats their young.