Six-spot burnet moths

See six-spot burnet moths emerging in the Museum Widlife Garden © Derek Adams

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Toxic talents of Britain's cyanide moths

Drowsy caterpillars are transforming into moths with a cunning skill - producing their own cyanide. 

Plump in their yellow cocoons, caterpillars of six-spot burnet moths have been pupating in the Museum grounds.

And this common British species has started to emerge, complete with eye-catching red and black wings.

The red spots are a sign of a deadly talent. The moths are able to produce hydrogen cyanide - a chemical compound that gives them a bad taste and, in large quantities, can kill a predator.

Museum ecologist Larissa Cooper says, 'Six-spot burnet moths are a stunning, day-flying moth and it is fantastic to see them thriving in the grounds and in the Museum Wildlife Garden.

'If you look closely, you'll see their papery cocoons high up on the stems of grass and knapweed.'

Waking from sleep

With dark, faintly iridescent forewings bearing six bright red spots, the burnet moths (Zygaena filipendulae) are easy to spot against green grass.

The species is widespread in Britain and Europe, and it has hydrogen cyanide at every stage of its life cycle.

A caterpillar of the six-spot burnet moth

Caterpillars of the species grow round and plump after feeding

The caterpillar food is birdsfoot trefoil (Lotus corniculatus), a grassland plant that grows in the Wildlife Garden. When caterpillars feed on its leaves, they are able to metabolise toxins found inside the plant for their own use, without being harmed.

If the caterpillars do not get enough hydrogen cyanide from their food, they can produce it themselves.

The cyanide is also used as a mating tactic. Females can release plumes of the chemical, which is likely to combine with normal sexual pheromones and help attract males. Males can also transfer the cyanide to a female during mating.

Spot the species

The six-spot burnet moth thrives in grassland, and visitors to the Museum will be able to see it fly and lay eggs during July and August.

Caterpillars will then start feeding in autumn, before hibernating through the winter and pupating next spring.

Unlike many species of nocturnal moths, the six-spot burnet is active during the day, relying on its striking wings to warn off predators.

Larissa says, ‘It is great that the moths are pupating on the chalk downland in the Garden and are spreading around the grounds.

'They have also begun to breed along the grass in front of the Museum, which has been left to develop naturally and is managed as a grassland habitat.'

The species relies on grassland for survival, which is proving increasingly challenging in the British countryside as land is being used for transport and housing.

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