This butterfly is not what it seems, doubly so

A harmless mimic turns toxic.

The sometimes disgusting viceroy butterfly, Limenitis archippus.

Jeff Oliver/University of Arizona

Keen entomologists may well have already noticed that this insect is not a queen butterfly (Danaus gilippus), even though it looks rather like one. They will guess, therefore, that it is another species, a viceroy butterfly (Limenitis archippus), known mainly for its uncanny resemblance to a queen butterfly.

And they would be correct – but this butterfly has another secret.

Looking like another species is known as Batesian mimicry, and it’s a tried and tested evolutionary strategy. Typically, a Batesian mimic will look very much like a species that is toxic or ferocious or otherwise lethal – and thus gain a survival advantage because predators will avoid it.

Queen butterflies feed on willow trees and absorb the plants’ phenolic glycosides, making them highly poisonous to predators. Viceroy butterflies also feed on the willows, but retain the toxins past caterpillar stage.

Evolutionary theory suggests that this strategy will only work in areas occupied by both species.

Researchers led by Katy Prudic from the University of Arizona, US, however, recently made a surprise discovery. They examined viceroy butterflies in the north of Florida, where queen butterfies don’t live, and discovered that the viceroys had developed a method for holding on to their phenolic glycosides in adulthood – making them every bit as toxic and foul-tasting as the species they evolved to mimic.

In population terms, the results are good. Predators munching on a northern viceroy learn very quickly not to repeat the exercise.

The research is published in the journal Communications Biology.

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