Here we fly through the great and gruesome science of butterflies, down to tiny wing scales and the shine of their eyes.
Butterflies are seemingly fragile insects, fluttering off in fear if you interrupt their flower feast. Yet, from their outstanding vision, to their less-than-delicate beginnings, there’s a lot of science to unravel.
Even the colourful patterns and beat of butterfly wings are more than what meets the eye. Read on for everything we know about these bewildering creatures and how the science of butterflies has contributed to innovations in technology.
How long does it take for a caterpillar to turn into a butterfly?
We’ve all heard the story of The Very Hungry Caterpillar, who keeps eating and eating as it grows until it eventually transforms into a butterfly. But what’s the science behind the story and how long does it take to form a butterfly?
Like a Charmeleon-to-Charizard evolution in Pokémon, the caterpillar is an early form in the butterfly’s life. While living the sweet life of leaves and leisure, a caterpillar, which is the larva of the butterfly, keeps growing until reaches a ‘critical size’.
At this point, a rush of a hormone (ecdysone) is released. This signals to the little fellow it should shed its skin, or moult, over and over.
Though changing while it moults, it remains a caterpillar thanks to another set of hormones which stop it from developing any butterfly-like features. As well as digesting the plants and ants it’s been crunching on, a caterpillar must effectively digest itself before transforming into a butterfly.
This metamorphosis from the caterpillar to butterfly is generally known as the pupa. It’s a time of growth, change and, yes, a pretty gross digestive process (more on that in the next section).
This stage of the insect’s life cycle can last anywhere from a few weeks up to two years. The difference in timeframe depends on the particular species of butterfly.
What happens inside a cocoon?
A caterpillar’s chrysalis or cocoon is like a hardened sleeping bag, formed from the caterpillar’s own body.
To create these shells, caterpillars first anchor themselves onto a leaf or twig using stem-like appendages called ‘cremasters’. Using this, they hang themselves upside down from a branch or leaf in preparation for the transition. Some butterfly caterpillars have special glands in their mouth which releases a sticky silk substance to secure their chrysalis in place.
Once hooked, the caterpillar constructs the protective chrysalis casing from its own body. By shaking off its outer layer of skin again, it can zip itself up inside the sturdy casing.
Inside this tough casing is where the changes get really incredible and even more disgusting. Having had his fill of food outside the chrysalis, our caterpillar friend releases digestive enzymes. These get to work breaking down the tissue and muscle cells into what is best described as caterpillar soup.
Within this soup, some groups of cells outlast others, and not by chance. Before the caterpillar has chewed its way through your vegetable patch, it has already started developing specialised cells.
Remember that set of hormones preventing the caterpillar from changing too much as it sheds its skin? At this point, these hormones have diminished, and a second avalanche of ecdysone helps the specialised cells to flourish. These will go on to build the butterfly, forming its wings, eyes and more as they differentiate and grow.
How does a butterfly get out its cocoon?
Another hormone-controlled process, the emergence of a butterfly from its casing is not as simple just flapping its wings and breaking free.
When a butterfly is fully formed, it will release hormones which act to soften the shell and help the butterfly start moving. Often the shell will become transparent, giving us a peek at the newly formed creature inside.
Once the cocoon is softened, the butterfly can begin to crack it open. It does this by inhaling air and expanding its wings. It can then push through with its legs and crawl out and continue hanging until its wings dry and spread. One hell of a stretch after being curled up inside.
How long do butterflies live?
Although they can be found all over the world, butterflies have a fleeting life. With an average lifetime of around three to four weeks, most butterflies don’t have long to explore.
However, it varies across different species. In 2009, scientists did a large-scale study and found that butterflies’ lives span from a few days to almost a year.
Where do butterflies live?
Butterflies can be spotted flapping around in almost any habitat. Scientists have observed butterflies in the Arctic, with some seen exploring the tundra in the ‘warmer’ days, between 15 and 18°C. Like rats, the only continent butterflies can’t be found is Antarctica due to its sub-zero climate.
Monarch butterflies have a longer lifespan than most and will take flight from their native USA and Canada habitats to the warmer climate of Mexico for winter. Some migrating monarch butterflies travel over 4800km to reach their warm winter home.
Unlike birds, butterflies don’t nest – but sometimes their caterpillar babies do. Butterflies will find the perfect plant to home their eggs and if enough are laid together, the caterpillars get constructing.
Scientists have seen that when groups of caterpillars hatch on the same plant, they will work together and build a tent around their plant. With their trusty silk, they tie leaves together to create a little caterpillar home. However, it’s the rare butterfly whose caterpillars will pitch camp. Since these special silk glands are needed, you are more likely to find a moth’s caterpillars building a silky home.
Can metamorphosis happen in space?
In 2009, NASA put butterflies to the test, launching several caterpillars into orbit and tracking how they develop in microgravity. Microgravity creates almost weightless conditions, and yet the team observed metamorphosis of the Monarch and Painted Lady butterflies in space.
With a little difficulty, the butterflies managed to emerge, bumping into the sides of their habitat and struggling to fully expand and dry their wings as quickly as they would here on Earth.
Though they can’t chew and savour their food, butterflies do still taste – with their feet. While all our taste buds are inside our mouth, butterflies have them across their wings, feet, antennae as well as their proboscis.
Gaining a taste for what is under your feet would not be nearly as exciting as flying, even if it’s mostly nectar. But, scientists studying these explain that butterfly taste receptors don’t just detect sweetness, they also help them distinguish between nutrients and deterrents, probing the plants.
By touching base with the plants, the taste receptors on a butterfly’s feet send a stream of biochemical signals, letting the butterfly know if a plant is a no-go for laying their eggs. Science suggests that butterflies associate bitter tastes with toxins, sticking with the nectar they know and love.
While a person’s sweet tooth may not be healthy, butterflies’ sweet feet can be life-saving.
Where do butterflies sleep?
Butterflies are day insects and set up camp to sleep hanging upside-down from leaves. This isn’t just nostalgia for their chrysalis days, hanging on leaves actually protect them from rain and any early morning birds looking to catch a little more than worms.
Butterflies enter a ‘low metabolic state’ at night to conserve their energy and digest food like humans. Scientists differ in their definitions, so this behaviour may simply be a good night’s rest, rather than sleep.
Butterflies with ‘warning colours’ like the orange and black of the monarch and the long-winged tiger and zebra butterflies are less concerned with hiding while they snooze. These colours indicate to predators that they will be poisonous to eat, as they have evolved to store the toxins from the milkweedeaten as caterpillars.
How do butterflies fly?
First, they have to be warm. As cold-blooded creatures, they rely on external sources to regulate their temperature and they can’t take to the sky until their body temperature is around 30°C. So if you see a butterfly bathing in the sun, it’s not getting a tan but warming up its wing muscles.
We have known for years that butterflies wings collide, but just how they fly so well with such a tiny body was a mystery until recently. In early 2021, a team of Swedish scientists shared that butterflies do not flap their wings when flying, but in preparation for flying.
Studying butterflies in a wind tunnel, they observed a distinctive wing clapwhere they collect and use air. According to the researchers, these butterflies form a pocket and use air to help power their flight.
“It was not exactly what we previously thought, the wings move in a very interesting way. In particular, they have these sort of have cymbal wings,” says Professor Per Henningsson, an evolutionary ecologist who published this work.
Source: BBC News