glance. "People say, 'How do you know that?'" he smiles. "A wasted life, really." Today, he and Meredith pack 44 caterpillars, housed within their tiny boxes, into a margarine tub, and head to the site.

Thunder rumbles overhead. "And God was not happy about the prospects of large blues on the common," quips Simcox. But, actually, it is perfect: the rain encourages the ants to forage, increasing the likelihood they will find a caterpillar. Before the rains came, Simcox sprayed ants' nests with water to induce them to come out. But prolonged drought can still spell disaster for the large blues. During the recent heatwave, Simcox became uncharacteristically gloomy: without rain, the ants stay in their nest and eventually resort to eating their own grubs, including the grub-impersonating largeblues.

In the meadow, Simcox scuffs the earth, another ploy to encourage the ants to come out, and Meredith taps a plastic box so that one tiny caterpillar pops out. It is a pale purple colour against the exposed earth, perfectly disguised when eating thyme flowers.

Simcox and Meredith carefully deposit the next caterpillar five metres away. "This is a monster. It's a leviathan of a large blue caterpillar," says Simcox delightedly. It is still just a few millimetres long. If the caterpillars are placed too close together they would be taken into the same nest and end up competing for food. Within seconds, an ant trundles towards the caterpillar, irresistibly lured by its sweet scent. Soon the ant will be "milking" it for this liquid, and will then misguidedly