Lisa Hanson

In 1979 Britain's most beautiful butterfly went extinct because the country had killed its rabbits and taken its sheep off the hills, and the scientist who worked out why had to put a flock back to bring the insect home. The large blue is a thing of chalk and limestone downs, and it has the strangest life of any animal in these islands. The caterpillar feeds on wild thyme for a few weeks, then drops to the ground and does an impression of an ant grub so convincing that a red ant carries it underground, where it spends ten months eating the ant's own young. Only one species of ant will do it, and that ant only lives in turf cropped so short the sun can warm the soil to the depth of its nest. Short turf means grazing. For a thousand years the grazing was sheep, and from the eighteenth century it was rabbits as well, millions of them, mowing the downs to a lawn. In 1953 myxomatosis arrived and killed ninety-nine rabbits in a hundred. Hill sheep were already coming off the downs as the farms went to the plough or to subsidy. Within a few years the turf grew long and cool, the ant died out of it, the caterpillar was carried underground by the wrong ant and eaten, and the butterfly dwindled through the sixties and seventies while everyone blamed collectors. The last British colony, in Devon, died in 1979. Jeremy Thomas spent the decade on his knees in the grass before he understood it. The whole chain ran back to a mouth cropping a hillside. In 1983 the butterfly was reintroduced from Sweden onto a Somerset slope where the first thing the project did was put the cattle and sheep back on, hard, and the ants returned, and the large blue came after them. It is now on thirty sites, every one of them grazed on purpose. A butterfly the colour of the summer sky disappeared from England for want of a sheep, and the people who saved it did not plant a flower or build a fence. They hired a grazier.