| The six-spot burnet moths complete their transformation|
|Moths cling to a knapweed flower as if it were a life-raft floating in the wreckage of the day. The six-spot burnet moths have hatched. How the caterpillars decided on which day in spring to climb the grass stems, spin papery cocoons around themselves and trust there would be a future summer in which to fly, is hard to fathom. But they did. They may have had no choice other than to follow the ancient impulse of their metamorphosis but their gamble on timing paid off. Out of their bivouacs in the grass struggle black, wizened creatures that seem to have crawled from a gothic imagination and have nothing to do with the plump, lemon-yellow, black-dotted caterpillars that went into them.|
Although this magician's trick of pupation – two separate creatures in the same body cabinet – seems complete, the moths have brought something with them from their past lives: hydrogen cyanide, or HCN. Burnet moth caterpillars absorb HCN from the glucosides in their food plants: bird's-foot trefoil and vetches. They can also synthesise HCN themselves, storing it in body cavities and excreting it as chemical weaponry.
As the club-headed moths emerge, their wings relax and expand, glossy black with risque scarlet insignia. This burlesque exhibitionism warns that these moths are at best unpalatable. After one bite predators learn to leave well alone. It also represents a form of mimicry, where other black and red moths such as the cinnabar – which contains alkaloids from ragwort notorious for poisoning horses – flaunt the same message.
Interestingly, burnet and cinnabar moths use black and red as adults and yellow and black as caterpillars. But to compound their magic, the six-spot burnets have synchronised emergence this evening with the opening of their favourite greater knapweed flowers into an extraordinary summer where anything seems possible.