Colourful moths and their role as artful dodgers in late summer

Six-Spotted Burnet Moths

Six-Spotted Burnet Moths - Credit: Archant

The colourful moths we see in late summer have some cunning ploys to deter predators, from wing displays designed to dazzle and play optical tricks to oozing poison on their enemies, says Professor Philip Howse

Cinnabar Moth

Cinnabar Moth - Credit: Archant

Moths have the art of a magician when it comes to camouflage. Think of a moth and you may have an image of a dull grey or brown triangular thing, looking like a dead leaf below the porch light. But not all are like that. Many are exquisite mimics of bark, lichens, broken twigs, dry grasses, dead leaves and fungi while others are as brilliantly coloured as any butterfly.


Cinnabar Moth

The colour red is a powerful signal for us but most animals (including bulls) do not see red. For them is just one of the hundred (not fifty) shades of grey. However insects and birds, which are the main predators of butterflies and moths do see it, and we can see it particularly clearly against a black background. It’s no surprise then that the Cinnabar Moth (Tyria jacobaeae) is so conspicuous when it takes wing in the sunlight, like an animated rose petal of the deepest red. Despite the name, the scarlet pigment is not cinnabar - a toxic mercuric ore used for decoration in ancient cultures. It is more likely to be cinnamic acid - a red colourant used widely today - derived from the aphid-like cochineal insect which was imported into Spain in the 15th century by the Conquistadors.

Although cochineal is harmless, the cinnabar is very poisonous - cyanide oozes from glands behind its head. Its caterpillar is no less lethal; it feeds on ragwort, the plant that kills cattle and horses if they graze on it. Its yellow and black wasp stripes advertise that it is full of toxic alkaloids, although the caterpillar is immune to them itself.


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Tiger Moths

In his poem St Agnes Eve, Keats describes the bed-chamber of the demi-goddess Madeline with reference to vibrant images and colours, including those of a moth:

‘A casement high and triple-arch’d there was, All garlanded with carven imag’ries Of fruits, and flowers, and bunches of knot-grass, And diamonded with panes of quaint device Innumerable of stains and splendid dyes, As are the tiger-moth’s deep-damask’d wings.’

Unless you have seen a tiger moth, and probably many poetry lovers have not, the vivid allusion to lustrous red- and blue-dyed damask silk will be lost on you. But in the summer and you can see such brightly coloured moths. The Garden Tiger Moth (Arctia caja), for example has wings patterned like a brindled cow, breaking up its shape and outline. Disturb it and you have a shock and awe effect as it exposes its hind wings with iridescent blue spots on a red background. Advertisers avoid using blue print on a red background, and the converse, because blue and red focus at different levels on the retina and produce a strange dazzle effect. The moth’s display is designed to startle predators and to warn them that this creature may be poisonous.

Keats, however, was more likely to have had in mind the Scarlet Tiger Moth (Callimorpha dominula) which sometimes flies by day and has deep crimson hind-wings. The image above was taken with the moth on a window pane, and the back lighting reinforces colour of the brilliant silky hind-wings producing a deep numinous colour that surely was the poet’s inspiration.


Burnet Moths

On chalk and limestone downs in July and August you cannot fail to see iridescent Burnet Moths flying like black red-winged bees in the day time. The famous entomologist Dame Miriam Rothschild tested one for palatability and nearly died. She later found that it produces hydrocyanic acid - a deadly poison for any insect predator.


Burnished Brass Moth

The aptly named Burnished Brass Moth (Diachrysia chrysitis) has another clever strategy to avoid predators. Like the polished brass and purple vestments in a church, its delicate colours glisten in the light. Usually in the darkness of foliage it stays hidden but when disturbed it fans its wings producing a shimmering reflection that is likely to startle and confuse any predator, and give it an escape route. The iridescent colours are produced by internal reflections in the scales that line the wings in a similar manner to those produced by a soap bubble.


Magpie Moth

Nocturnal predators do not see colours, so camouflage colours are only needed for moths that hide from birds during the day. There are some brightly coloured moths, though, that fly in the daytime if they are disturbed. One of these is the Magpie Moth (Abraxas grossulariata) which has wasp banding on its body and bright wings which are, remarkably, embroidered with pictures of its caterpillar - a “looper” with the same orange and black blotchy patterns. The reason is simple: both the caterpillar and the moth are poisonous, so any bird that has tried eating this moth’s offspring will tend to avoid them when they become adult.


About Philip Howse

Professor Philip Howse taught animal behaviour and entomology at the Universities of Cardiff and Southampton. His research took him to countries including Brazil, Venezuela, Mexico, Nigeria, Malaysia, the West Indies and India. He invented methods of controlling insect pests of horticulture and agriculture without the use of synthetic pesticides, for which he received various awards including the OBE and a Prince of Wales Award for Innovation. His books include Butterflies, Messages from Psyche and (with Kirby Wolfe) Giant Silkmoths; Colour, Mimicry and Camouflage (both published by Papadakis). He is currently working on his next book The Vicar of the Amazon, The Reverend Miles Moss about a Victorian butterfly collector, artist and musician.


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