Toughest Butterfly On The Block

Peacock Butterfly

We don’t tend to think of butterflies as being formidable, intimidating creatures, but there is one UK butterfly that can send mice scurrying, terrify chickens and cause bats to retreat with a mere flick of its wings. This fearsome monster is...(cue scary music)...the Peacock butterfly.

How can a Peacock butterfly repel animals many times its own size, particularly during winter when dormant insects are at a severe disadvantage against hungry, warm-blooded predators?

Peacocks are not poisonous or foul-tasting, so their first line of defence is to go unnoticed. The Peacock, like other butterflies that overwinter as adults, is a master of disguise. At rest, with its wings held tightly together over its back, the Peacock resembles a dead leaf. Dark colours on the underside of the wings and a scalloped, irregular shape provide convincing camouflage. Remaining motionless is a key part of this strategy. Comma butterflies take this to the extreme, remaining quite still even when a predator is touching them. If a predator sees through the Comma’s disguise though, the butterfly will be eaten.

Peacock butterfly wings shutPeacock butterflies however, have another, more dramatic trick up their sleeve, or rather, on their wings. When a predator gets close the Peacock will abandon its disguise and adopt shock tactics instead, repeatedly flicking open its wings, to expose suddenly bright upperwing colours and its characteristic, large eye-spot markings.

It’s these eye spots, of course,  that gave rise to the butterfly’s vernacular name. It was originally known as the Peacock’s Eye, a clear reference to the ‘eyes’ on the extravagant tail feathers of the male Peacock bird. Experiments have shown that the eye spots on the Peacock butterfly’s wings startle small insectivorous birds, such as Blue Tits, greatly increasing the butterfly’s chance of surviving such an encounter. Small Tortoiseshells, which also flick open their wings to reveal bright colours, but do not possess eye spots, are much less successful at warding off predators.

Whether birds mistake the Peacock’s eye spots for the real eyes of a much bigger (and potentially dangerous) animal such as an owl is not clear. Some scientists have argued that it is simply the brightness and boldness of the design that instils wariness in small predators. However, recent studies found that chickens are also frightened by the display of Peacock butterflies and sometimes uttered alarm calls that are normally used to warn their flock about ground-based predators.

Interestingly, Eyed Hawk-moths also gain some defensive advantage from the large eye spots on their hind-wings, but are also much less successful at repelling bird attacks than Peacocks, despite their larger size (wingspan and body weight). This difference may be due to the vigorous wing-flicking performed by Peacocks, repeatedly revealing the eye spots, compared to the more passive display of the moth.

But the Peacock has other weapons in its arsenal too. When it flicks its wings open it produces an acoustic display as well as a visual one. Special sections of the forewing and hindwing rub against each other making a hissing sound audible to humans, and at the same time a small part of the forewing membrane buckles producing ultrasonic clicks. It would seem that these sonic defences target mammalian predators. The ultrasonic clicks, for example, are above the hearing range of birds, but have been shown to elicit reactions in bats.

More evidence is required to test whether Peacock butterflies really do have an effective defence against bats, as is found in some sound-producing moths. However, the sounds produced by the butterfly do appear to deter mice. Mice and other small mammals are thought to be important predators of hibernating butterflies such as Peacocks and Small Tortoiseshells. Experiments in total darkness show that Peacocks perform their wing-flicking display when touched by foraging mice and that both the wing flicking itself, but also the noises produced are effective deterrents against these predators. Small Tortoiseshells also produce sound during their wing-flicking display, but suffer higher predation by mice perhaps because they rely more on the camouflage strategy and use wing-flicking less readily.

So the secret to the Peacock’s success appears to lie in having an array of different tactics to deploy against different predators and in different situations. Its use of camouflage, switching, when danger threatens, to an aggressive, visual and auditory display doesn’t guarantee it protection in a hungry world, but it certainly gives it an edge and, to my mind, earns it the title of the toughest UK butterfly.

Richard Fox
Surveys Manager
Follow me on Twitter: @RichardFoxBC