Butterflies might appear to be simple, ethereal insects, but don’t be fooled – they are secretly masters of disguise. From eyespots to mimicry, the markings on butterfly wings serve important functions that range from warning of their toxicity to the attraction of mates. Although butterfly markings vary vastly, the way they forge these markings is always the same. Every pattern is a technicoloured mosaic of microscopic scales. These scales are coloured by fractured pigments, which alter the wavelength of reflected light to produce a rainbow of iridescence. Birds, spiders, wasps, mice, slugs and many other animals eat butterflies, so deceiving these predators is particularly important for their survival.
Eyespots like those of the Peacock Butterfly serve multiple functions. They can trick smaller predators like mice into thinking they are owls. They also act as decoys, encouraging birds to attack only the tips of their wings and not their more vital body parts. Birds generally attack the head first to ensure that their prey doesn’t escape. Under low light conditions, the contrast on a butterfly’s wing markings is greater than that of their eyes, so birds will attack these spots instead. Butterflies have no feeling or circulation in their wings, which can still fly perfectly well even when damaged. Eyespots become particularly effective in the early morning, when birds are most actively foraging and butterflies’ bodies are still too cool for flight, leaving them vulnerable to attack.
Instead of decoy markings, many butterflies use camouflage to blend in with their surroundings.
For example, the Indian Leaf Wing Butterfly looks just like a dead leaf, complete with spots of mould and worm holes. However, a flutter of its wings reveals an exuberantly coloured blue and orange butterfly. This contrast is an interesting example of a compromise in the evolutionary trade-off between natural selection (avoiding being eaten) and sexual selection (finding a mate). Famous naturalist Alfred Russell Wallace used this example to support the theory of evolution.
Camouflage as a leaf might seem like the ultimate act of concealment, but the Glass Wing Butterfly has a better disguise. The ‘invisible man’ of the butterfly world, this diminutive insect has no scales on its wings, making it completely translucent – even in captivity they are almost impossible to spot.
Hiding in plain sight
In contrast, the aptly named Zebra Mosaic Butterfly’s geometric black and white swirls may seem like a terrible idea for an animal trying to disguise itself. Like the black and white ‘dazzle camouflage’ used by naval fleets during the Second World War, these markings break up the shape of the wing, making the size and direction of travel difficult for predators to determine. Studies have shown even a simple pale band of colour on darker wings creates the illusion of false boundaries. This strategy is known as ‘disruptive camouflage’.
The imitation game
It’s not just adult butterflies that are experts in concealment. Caterpillars of the Swallowtail family mimic bird droppings, whilst their chrysalises also disguise themselves as leaves.
The most callous butterfly trickster is the caterpillar of the Large Blue, which imitates the noise made by a queen ant as well as the chemical scent of ant larvae. Upon finding a caterpillar, the gullible ants take it back to their nest and feed it, where the sly caterpillar scoffs ant larvae until it is ready to pupate… and you thought cuckoos were bad!
The selective pressure of predation at every stage of a butterfly’s development has rendered disguise an absolute necessity. Their deceptive mechanisms have evolved over 45 million years, and are part of the reason over 20,000 species of butterflies exist across the world today.
Unfortunately for the wonderful butterfly, human activities are changing the niche environments to which these adaptations are so finely tuned. At the current rate, it won’t be long until they’re rendered effectively useless.
The Natural History Museum’s ‘Sensational Butterfly’ exhibition is now open daily from 10am-5.50pm. For more information go to: http://www.nhm.ac.uk/visit/exhibitions/sensational-butterflies.html.
Rosemary Cafferkey is studying for an MSc in Science Communication.
Images: Butterfly, Anna Omelchenko; Peacock, captiva55; Indian Leaf (closed) Danny Heilprin; Indian Leaf (open), bearacreative; Glass Wing, Marcio Jose Bastos Silva; Zebra Mosaic, Doug Schnurr; Swallowtail chrysalis, entnemdept.com; Large Blue pupa, planet earth.com.