The Oldie: Profitable Wonders – May 2011
The Ant and the Butterfly
The Large Blue butterfly is in truth not very large at all, its two inch wing span being only slightly greater than that of the Common Blue. It does, however, occupy a special place in the affections of all lepidopterists by virtue of its unusual life history which ranks amongst the strangest of any creature. In the last week of June and early July the female deposits her miniscule pearl like eggs on the petals of wild thyme flowers from which the caterpillar form emerges to feed on their downy blossom. Then the caterpillar, after its third skin-casting, becomes restless, drops to the ground and begins to walk,’as though’, comments naturalist E L Grant Watson,’ it wants something but is not quite sure what’.
The caterpillar walks and walks until it meets and is recognised by a red ant of the species myrmica sabuleti who starts to caress and stroke it with feet and antennae to which it responds by secreting from a pore on its tenth segment a sweet honey-like dew much to the ant’s liking. After a time,’prompted by some unexplained and mystic sympathy’, the caterpillar rears up—a signal it wants to be carried off. The ant seizes it gently in its jaws and heads for its underground home placing it in one of the chambers where its own progeny, the young ant eggs and larvae are being nurtured—and on which the caterpillar will feed, while continuing to produce its honey dew secretions as payment for its hosts’ generous food and lodging.
They hibernate together for the winter, and come the spring, the caterpillar pupates forming the chrysalis from which it will emerge as a butterfly, its wings at first unexpanded, like limp and shrivelled leaves drooping on each side of its body. How unlikely a place—the dark underground of an ant’s nest—for a butterfly to find itself.
And then the hosts, in a final act of inexplicable altruism, escorts this one time devourer of their children through the dark passages of their home up towards the light, encircling it to ward off any predators as the butterfly fills the veins of its wings with its pale yellowish green blood. And off the Large Blue flies for the few short weeks of its adult existence, just time enough to seek a mate and produce its eggs, before the life cycle starts over again.
That transition from egg to adult depends on so many bizarre and fortuitous events, its seems astonishing that the Large Blue exists at all—and indeed just over thirty years ago it became extinct in Britain. But that is not the end of the matter, for when Jeremy Thomas, Professor of Ecology at Oxford University sought to reintroduce it back into this country, he discovered its survival is predicated on several other factors—not just colonies of red ants in close proximity, but as they are heat dependent, that the grass is kept short by grazing animals so as to warm the soil. Nor can the summer be too hot, as rain encourages the ants to forage—thus increasing the likelihood of that chance encounter with the caterpillar.
It has taken Professor Thomas the best part of a decade of intense effort to recreate the right ecological balance for butterfly and ant to renew their surprising relationship—and now once again the Large Blue can be seen fluttering across the meadows of Devon and Somerset. “The extravagant idiosyncrasies of its life,” suggests Grant Watson should cause all’to pause and wonder’.