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Amazing Metamorphosis:
an Inside Look at the Life Cycle of Butterflies

There are a staggering number of butterflies and moths in the world. A 2003 survey suggests there are nearly 265,000 species. They are found in a variety of habitats and some species, like the monarch butterfly, migrate over great distances.

Both butterflies and moths are arthropods and are classified as Lepidoptera; a name derived from the Greek words meaning “scale” and “wing.” Lepidoptera are different from other insects. Their entire bodies are covered with overlapping scales, much like shingles on a roof. The scales are so small and so thin that it would take more than half a million of them stacked on top of one another to reach an inch in height.

Like all insects, butterflies and moths have three body parts: head, thorax and abdomen. On the head are two compound eyes, a pair of antennae and a coiled feeding tube or proboscis. The antennae are sense organs used for smelling and for balance. An adult butterfly has no jaws, so it uses its proboscis to sip liquid from flowers, other insects, decaying fruit, fermenting sap or even decaying carcasses. The compound eyes of butterflies and moths are sensitive to color and movement and also can see ultraviolet light.

No single feature separates butterflies from moths, but there are a few general ways to distinguish between the two. Butterflies typically fly by day; moths tend to fly at night. Butterflies hold their colorful wings upright over their backs. Moths hold their wings parallel to their bodies. The antennae of butterflies have knobs on the ends. Moths’ antennae are more intricate, sometimes feather-like, structures.

It’s a butterfly’s life
A butterfly’s lifecycle is one of constant change known as metamorphosis. The lifecycle of a butterfly consists of four distinct phases: egg, larva, pupa and adult (or imago).

During the search for a mate, butterflies can recognize potential partners and possible rivals through a combination of color, wing beat speed, flight patterns and pheromones. Pheromones are chemicals that stimulate excitement or arousal and are produced by male butterflies and female moths. The male butterfly flutters around the female, waving his wings and releasing pheromones. The male and female will alight and link together in a tail-to-tail position.

The fertilized female finds an appropriate host plant by sight and then tests it by smell using special sensors on her feet. Her offspring will only be able to eat the foliage of specific plants, so she must select the correct plant or her children will starve. Different species of butterflies lay eggs differently; some lay eggs singly, some lay eggs in clumps and others may scatter eggs while in flight. As the eggs get ready to hatch, they turn dark and the caterpillar inside can be seen.

When it’s ready to hatch the larva (or caterpillar) inside the egg cuts a circle in the egg with its jaws and emerges – an absolute eating machine. The job of the caterpillar is to eat, grow and not get eaten in the process. This larval stage may last from 12 days to eight weeks or more, depending on the species. As the caterpillar grows larger, its exoskeleton becomes too small. The larva grows a new, soft skin beneath the outer one and then sheds the upper skin. Caterpillars molt an average of five times before moving on to the next phase of its development.

Caterpillars are slow-moving morsels of protein and fat and are tempting treats to a variety of other animals like birds, bats, lizards, frogs and even other insects. As a result, caterpillars have adapted a variety of strategies to avoid becoming an easy meal. Some caterpillars are camouflaged; others are poisonous or very distasteful and advertise this fact with bright coloration. Some have developed displays like false eyes, flash marks and unpleasant aromas to warn off predators.

After its final molt, the caterpillar empties its digestive system and the exoskeleton seals shut. Some caterpillars weave a silk girdle around their bodies to help hold them in place while others enclose themselves entirely in cocoons. When the caterpillar’s position is secured, it begins to wiggle until the skin along its back splits. Underneath the caterpillar’s exoskeleton is a casing, called a chrysalis. The chrysalis is just another type of exoskeleton. Once the chrysalis casing is exposed to the air, it hardens. From the outside, the chrysalis looks inert, but inside it’s a cauldron of activity.

Two or three weeks later (sometimes longer), a new creature emerges.

The emergence of an adult butterfly from its chrysalis is called eclosion. The emerging insect uses both air pressure and blood pressure to expand its body spaces. Gravity helps its wings unfold. Each crumpled wing is actually composed of two thin sheets, or membranes, that are bonded together with hollow veins between them. As blood drains into those veins, the folds in the butterfly’s wings are pulled flat. After 10 or 20 minutes, the wings expand to full size, but the butterfly’s outer skeleton is still very soft. When the expansion phase is over, the butterfly holds its wings apart for an hour or so until they dry and harden. If a butterfly is damaged during its expansion phase, the unexpanded or injured parts will harden and the butterfly will be crippled for life.

In many species, the male butterflies emerge about a week before the females. This gives the males time to seek out nectar to build the energy reserves needed to find a mate. After an adult butterfly (or imago) emerges, the search for a mate begins and the entire process is repeated. Adult butterflies can live for a few weeks to several months; in some species, the adults can live for up to a year.

Butterfly conservation
In the past, collectors were the biggest threat to rare butterflies. Today, habitat destruction and pesticide use are the greatest threats butterflies face. Butterflies and moths are dependent on specific host feeding plants, some that are considered weeds by humans. Draining swamps, destroying woods and other natural living habitats remove the butterflies' basis of life. Pushing back or removing quantities of butterfly feeding plants has fatal consequences for them.

The numbers of extinct butterfly species have increased. However, people are learning from their mistakes and efforts to protect butterflies are underway.

A great deal of attention has been given to the destruction of the world’s rainforests by villagers in other countries who need to make space for agriculture or need the money from logging. Many groups are helping to reduce this destruction by teaching natives to farm butterflies. Butterfly farming helps to save the rainforest by providing villagers an alternate income other than clearing virgin tropical forest. Raising insects to sell is the only incentive some indigenous peoples have to save their tropical forests. Butterfly specimens come from butterfly and insect farms in Australia, Asia, North, Central and South America which breed and supply live and non-live insect specimens for butterfly houses and insect collectors around the world. Butterflies and insects live their entire lifespan on these farms, and produce eggs for the next generation. This profitable enterprise promotes important habitat conservation, and many of the butterfly species exhibited in the Butterfly Garden came to the Aquarium from these farms.

Plant a butterfly garden
Home gardeners can create their own habitats for native butterfly populations. Providing a habitat for native butterflies is one way to help regional butterfly populations. The National Wildlife Federation provides the following tips to help backyard gardeners get started:

  • Provide flowers to feed adults
    Dense "clusters" of small flowers such as zinnias, marigolds, tithonia, buddleia, milkweeds, verbenas and many mint family plants generally work well.
  • Plant good nectar sources in the sun
    Key butterfly nectar source plants should receive full sun from mid-morning to mid-afternoon. Butterfly adults generally feed only in the sun. If sun is limited in your landscape, try adding butterfly nectar sources to the vegetable garden.
  • No insecticides
    Insecticides such as Malathion, Sevin, and diazinon are marketed to kill insects. Don't use these materials in or near the butterfly garden or better yet, anywhere on your property. Even "benign" insecticides, such as Bacillus thuringiensis, are lethal to butterflies.
  • Feed butterfly caterpillars
    If you don't "grow" caterpillars, there will be no adults. Bringing caterpillar foods into your garden can greatly increase your chance of attracting unusual and uncommon butterflies. In many cases, caterpillars of a species feed on only a limited variety of plants. Most butterfly caterpillars never cause the leaf damage associated with moth caterpillars such as bagworms, tent caterpillars, or gypsy moths.

The Tennessee Aquarium inspires wonder and appreciation for the natural world. Admission is $17.95 per adult and $9.50 per child, ages 3-12. Each ticket purchased helps support Aquarium conservation programs. The IMAX® 3D Theater is next door to the Aquarium. Ticket prices are $7.95 per adult and $5.50 per child. Aquarium/IMAX combo tickets are $21.95 for adults and $12.50 for children. Advance tickets may be purchased online at www.tnaqua.org or by phone at 1-800-262-0695. The Aquarium, located on the banks of the Tennessee River in Chattanooga, is a non-profit organization. Open every day except Thanksgiving and Christmas, the Aquarium and IMAX are accessible to people with disabilities. Members enjoy unlimited visits and other benefits. Call 267-FISH to join.

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