Butterflies: the science behind the colour
Butterflies and moths are masters of disguise, able to copy animal faces, rolled-up leaves and even snakes.
Welcome to the kaleidoscopic world of the butterfly wing.
How do butterflies and moths (known collectively as Lepidoptera) make use of their vibrant wing patterns? Why are some species experts in camouflage? Museum Microlepidoptera curator Dr David Lees explains.
There are more than 18,000 named butterfly species on the planet today, and about 140,000 different moth species. All of them evolved from a common ancestor that lived more than 225 million years ago.
From that one ancestor, a parade of colours and shapes have burst forth, populating forests, savannahs, fields and gardens with patterns and textures. Each species has developed a strategy to make the most of their biggest asset and defining feature: their scaly wings.
Lepidoptera rely on colour in every aspect of their lives: sparring, courting, mating and hiding.
They can see more of the visible light spectrum than humans can - a little further into the red end of the scale. Like many insects, Lepidoptera are also able to see ultraviolet light.
David explains, 'This level of colour sensitivity is vital, not just for finding flowers but also for finding perfect camouflage backgrounds and for seeking out other butterflies. It is especially useful for fluttering after romantic partners and for sparring males.
'Postman butterflies use the striking red bands of colour across their wings to find each other. But then they use other tricks - maybe chemical cues - to avoid mating with other Heliconius species, which look to us almost exactly the same as the postman.'
A common use of colour is as a defence against predators. Some species have developed large eyespots on their wings, tricking predators into thinking they have come face to face with a much larger creature.
The owl butterfly is one example of this, and it can often be spotted in the Museum's Sensational Butterflies exhibition. Its yellow ringed eyespots look to us like the feathery face of an owl.
Whether this owl mimicry is intentional or not is still a contentious issue among scientists.
Some studies support the theory, but other scientists say that the effect actually makes the butterflies more conspicuous.
Another theory is that the butterfly looks like a gecko on tree trunks, which real geckos (a major predator of this species) would avoid.
David says, 'Wings sometimes bear patterns that conjure up other creatures. Our own eyes readily interpret them as something frightening - and it will also make a predator think twice.
'As a second line of defence, butterflies will flash their showy upper side patterns, which buys them the few vital seconds they need to escape. For example, the owl butterfly has contrasting blue and orange scales on the upperside.'
A stark warning
Another popular technique, known as aposematism, is for a butterfly to advertise its toxicity to predators by exhibiting warning colours.
The caterpillars of tiger moths and milkweed butterflies consume plants full of poisons and store them, making them taste disgusting to novice birds.
Bright, bold colours in the adults - often red or orange - then mark them out, warning birds to stay away next time.
Others don't bother eating toxins, opting instead just to copy the noxious species. The common African mocker swallowtail (Papilio dardanus) is one of the best in the world at this game. Females can mimic the wings of up to five different, more poisonous butterfly species, giving them protection.
Some butterflies and moths hide in plain sight, disguising themselves as leaves or twigs.
The Indian leaf butterfly (Kallima paralekta) is nearly impossible to spot when it is nestled among leaves.
Its upper side is steel blue with an orange band. However, the underside is a dull brown, appearing just like a dead leaf - complete with veins and a midrib. It can lie motionless among foliage or on the ground, entirely undisturbed.
David says, 'The disguise is so good that birds can completely overlook such resting butterflies.
'Even more incredible than the Indian leaf is an oriental moth, Uropyia meticulodina. It looks just like a rolled-up, dry leaf, but the wings are actually flat. The curling illusion is produced by an effect called countershading - in this case due to an exquisite blending of light and shadows.
'Natural selection has airbrushed the wing, rendering it in three dimensions. It is a process that must have taken millions of years of predation to perfect.'
The colours that we see on most butterflies have usually taken millions of years of evolution.
But some species are able to change colour within a generation or two, as the environment around them changes.
The African squinting bush brown (Bicyclus anynana), native to South African savannahs, has very small eyespots during the cool, dry season. It hides from predators and stays relatively inactive.
It doesn't live long, so several generations are produced during one year. The onset of the rains and the hot, wet season triggers a change: its eyespots become much bigger.
The air temperature and humidity surrounding the developing caterpillars determines what colour pattern the next season's adult will develop into.
David says, 'It's a remarkable example of the astonishing flexibility of butterfly colour patterns.
'These creatures can blend in perfectly with their surroundings in the dry season. When it's warmer and they are flying more to feed and reproduce, a generation emerges with conspicuous eyespots.
'These deflect attacks of birds and lizards away from the body.
'Colour is not there just to look stunning. It has an important job for most butterflies and moths, giving them a vital helping hand in the fight for survival.'