How Butterflies Work

A butterfly starts its life as a caterpillar, which hatches from an egg, eats voraciously and eventually sheds its skin to reveal a chrysalis. The chrysalis is a protective shell in which the caterpillar becomes a butterfly. By the time the butterfly emerges, or ecloses, it doesn't look much like it did when it formed the chrysalis. Its body has the same basic parts -- a head, a thorax and an abdomen -- but most of the similarities end there.

Along with its proboscis, a long, straw-like tube used for drinking, many of a butterfly's sensory organs are on its head. These include:

Not all of a butterfly's sensory organs are located on its head, though. At the end of each of its six legs, all of which attach to its thorax, are taste organs that the butterfly uses to find food. When a butterfly's leg touches a good food source, a reflex causes its proboscis to uncoil. This lets the butterfly retrieve and swallow the food, which is digested in organs in the butterfly's abdomen. A butterfly's reproductive organs are located in its abdomen as well.

A butterfly's most dramatic anatomical features are its wings. They're made of an extremely thin, transparent material called chitin stretched over a series of vein-like structures. The forewings are closer to the butterfly's head and are roughly triangular. The hindwings are closer to the tail and are shaped like fans or seashells.

The colors and patterns come from layers of tiny scales. It's easy to think of these as similar to fish scales, but they're structured more like short, tiny hairs. These scales protect the wings and provide insulation. Typically, the scales on the top of a butterfly's wings are brightly colored, while the scales and the underside are patterned for camouflage.

At first, the wings are wet and wrinkled. The butterfly has to expand and dry them as soon as it emerges from the chrysalis. To do this, it uses its body as a pump and forces fluid through a series of tube-like veins. It's a little like inflating a balloon -- as the veins fill with fluid, they slowly stretch the surface of the wings.

This is just one of the things a butterfly has to do as soon as it emerges to prepare for its life of flight. The butterfly also must also get rid of the waste produced during its transformation and the remains of its last meal as a caterpillar. This waste is known as meconium, and it has a bright red, often bloody appearance. Then, the butterfly has to thoroughly clean all its sensory organs so it can find food. Finally, it has to get its proboscis in working order. When the butterfly emerges, its proboscis is in two separate pieces that join together with tiny hooks and fringes. The butterfly has to curl and twist the two halves of its proboscis to create one drinking tube.

All this work takes place before the butterfly even takes flight, and it doesn't end there.

Whether a butterfly's body can function depends heavily on the weather. Strong winds and raindrops can damage butterflies' wings. Since butterflies have no way to repair wing damage, they usually find shelter when they sense changes in the weather that signal an oncoming storm. But temperature can be an even greater threat than rain or hail.

Butterflies' bodies work best at an internal temperature of about 82 degrees Fahrenheit (28 degrees Celsius). Butterflies can't move their wing muscles at all if they get too cold, which means they can't look for food or flee from predators. Many butterflies use the colors on their wings as a warning to predators -- they quickly flash bright colors or vivid, eye-like designs to startle a predator, and then they fly away. Butterflies can also show their colors to warn predators of their chemical defenses, such as toxins or foul-tasting compounds. In very cold weather, butterflies can't do any of this.

Unlike mammals, which can usually keep their temperature steady in all but extreme temperatures, butterflies have to use their surroundings to manage their body heat. And staying warm can be tricky. At night, butterflies roost, or take shelter, to protect themselves from the drop in temperature, but daytime is a different story.

During the day, you may see butterflies basking with their wings open to catch the warmth from the sun. In chillier temperatures, butterflies can also use their wings as reflectors, opening them partially to focus the sunlight onto their thorax, where their wing muscles attach. Sometimes, butterflies will rest on warm rocks to soak up the heat from underneath. If the weather gets too warm, a butterfly may fold its wings flat and arrange itself so the sun hits the narrow edge of its wings rather than the broad side.

Sometimes, the sun doesn't provide enough warmth to get a butterfly moving. When this happens, the butterfly can move its wings in tiny increments in each direction, gradually warming the muscles. This movement is a lot like how your body shivers in cold weather to keep you warm. Eventually, the butterfly's muscles warm up, and it's able to fly.

A butterfly doesn't get to stop worrying about temperature once it's in the air. Butterflies' bodies get colder as cool breezes move over them, just like a hot spoonful of soup cools off if you blow over its surface. This is why butterflies often fly in short, rapid bursts on very cool days. A butterfly will warm itself until it's ready to fly, move quickly to the next flower or basking spot, and begin warming itself again.

Not all butterfly journeys involve short hops from flower to flower. More than 200 butterfly species migrate over long distances. The most famous is the monarch butterfly, which makes its journey to overwintering grounds in California and Mexico in several stages involving multiple generations of butterflies.

Nectar is the staple of a butterfly's diet. In the plant world, nectar is a reward for animals that act as pollinators, including butterflies and bees. Flowering plants produce nectar that the insects want to eat, and in exchange the insects spread the flowers' pollen, allowing them to reproduce. While some insects, like bees, have lots of adaptations that allow them to carry lots of flowers, many butterflies don't. In fact, some butterflies don't spread pollen at all -- they take the nectar without helping the plant in exchange. In this sense, butterflies can be parasites.

It's easy to imagine butterflies as delicate insects flitting from flower to flower in search of nectar. Their long proboscis allows them to reach deep into flowers and retrieve the nectar found there. At first glance, the proboscis doesn't seem suited to consuming any other type of food. While it's true that sugary nectar is a primary source of energy for butterflies, they have lots of other dietary needs. Butterflies need nutrients and minerals to fly and reproduce, and many of these don't exist in the sweet liquids produced by flowers.

Some butterflies also eat fruit. Some of these butterflies pierce the fruit's skin and drain the juices from inside. Others drink the juices from the surface of rotting fruit. Butterflies that prefer to drink from fresh fruit sometimes have a pointed proboscis, making it easier to puncture the fruit's skin.

Getting enough minerals and salt requires other food sources, including urine, dung and standing water. This is why you'll often see many butterflies drinking from very shallow, still water. This water has absorbed minerals from the soil underneath it, and the butterflies need these minerals to supplement their diet. This behavior is called puddling. Sometimes, butterflies will fly away from a puddle and return to it a few seconds later -- this may disturb the water, bringing more minerals to the surface. If there's no water around, a butterfly may regurgitate into the soil and then drink in the hope of retrieving minerals.

All of these behaviors lead up to the main purpose of a butterfly's life -- reproduction. Read on to learn about mating rituals and how male butterflies contribute to females' ability to lay eggs.

A butterfly's life has four stages. It starts as an egg, typically attached to the underside of a leaf. The egg hatches into the butterfly's larval form -- the caterpillar. A caterpillar's job is to consume enough food to sustain itself during its transformation into a butterfly. This transformation takes place in the butterfly's pupal stage, when the butterfly is inside its chrysalis. Finally, an adult butterfly emerges from the chrysalis. While the larval butterfly was built for eating, the adult is built for mating.

Butterflies reproduce the way other animals do -- sperm from a male fertilizes eggs from a female. Males and females of the same species recognize one another by the size, color, shape and vein structure of the wings, all of which are species specific. Butterflies also recognize each other through pheromones, or scents. During mating, males use clasping organs on their abdomens to grasp females.

Many male butterflies deliver more than just sperm to their mates. Most provide a spermatophore, a package of sperm and nutrients the female needs to produce and lay eggs. Some males collect specific nutrients to produce a better spermatophore in an attempt to attract a mate. Some females, however, don't have a choice -- in some species, males mate with females before they have left their chrysalis or swarm the chrysalis waiting for the female to appear. In most species, males and females look a lot a like, but females often have larger abdomens for carrying their eggs.

Females store the sperm in a sac called a bursa until she's ready to lay her eggs. She fertilizes her eggs as she lays them, using the last sperm she received first. For this reason, males of some species will leave a substance that dries into a film on the female's abdomen in an effort to keep her from mating with other males. Females lay their eggs one at a time or in batches of hundreds depending on their species.

A butterfly has to take special care when laying eggs. The eggs must be kept warm and at the right humidity level. Too much moisture and the egg will rot or be attacked by fungus. Too little and the egg will dry out. Caterpillars also need to start eating as soon as they hatch, so most of the time the female places the eggs directly onto a type of plant that the caterpillar will eat. Typically, the eggs attach to the underside of a leaf, so they are hidden from predators. A few butterfly species use predators' nests, such as anthills, as protection, disguising their eggs with the pheromones the predators use to recognize each other.

In spite of all the effort female butterflies make to protect their eggs, very few make it to adulthood. Ants, birds and other animals can eat the eggs themselves, and caterpillars and butterflies are a popular snack for everything from birds to bats. Some insects also lurk in or around flowers to prey on adult butterflies. A butterfly's chrysalis also has few defenses from predators. And, at all stages of life, a butterfly can succumb to fungi and diseases.

If you've ever seen pictures of the famous annual monarch migration, you might think that monarchs are plentiful and in no danger of extinction any time soon. However, illegal logging in the protected Butterfly Biosphere Reserve, which houses part of the monarch's overwintering grounds, threatens the butterflies' survival. Without lots of trees in their overwintering grounds, monarchs have no place to hibernate or begin the next generation of butterflies.

Habitat loss is a serious threat to other butterfly populations, and not just in overwintering grounds. Urbanization and development can quickly destroy the plants where caterpillars eat and butterflies lay their eggs. In addition, some people view caterpillars as pests, especially when they destroy the foliage on carefully cultivated plants. For this reason, some people kill the caterpillars in their garden, preventing them from growing into butterflies.

Although butterflies are clearly not big-game species, human hunting has had an effect on their population. Some species are highly prized by collectors, and over-collecting has caused a sharp decline in their population. For example, several swallowtail species are on the U.S. Fish and Wildlife Service endangered species list in part because of over collecting.

Pesticides are another major butterfly threat -- adult butterflies are extremely sensitive to them. But keeping pesticides away from butterflies' food sources is easier said than done. Wind can carry pesticides far from their point of origin, contaminating butterflies' habitats. For this reason, people who want to encourage butterflies to live in their yards and gardens should rely on natural forms of pest control, such as encouraging the presence of pest-eating insects.

Fortunately, butterflies can live and grow in greenhouses and other indoor locations as long as they have food, water and the right plants. This makes it possible for nature centers and other facilities to care for butterflies and educate people, as well as to try to preserve some butterfly species. However, in spite of such efforts, habitat loss and pesticide use will continue to threaten butterflies worldwide.