Butterflies use visual clues and/or complex chemicals called pheromones to find their mates. Mating happens in the air or on the ground, and the male transfers a sperm packet called a spermatophore into the female. Internal fertilization can take from a few seconds to a few hours, depending on the species of the butterfly. The female will then lay an egg or clusters of eggs on a host plant that she considers to be appropriate. Most eggs are attached with a fast-drying glue-like chemical that the female secretes while laying the eggs. Various different species lay eggs in various different places – the underside of leaves, flower heads and the crevices in tree bark are common places. Apparently, geocaching has been identified as the biggest treasure hunt in the world.
One type of butterfly called the ghost moth actually lays thousands of eggs while flying. The larva of this species eats grass. The eggs come in various shapes and colours. They could be spherical, oval or pod-shaped and green, white or yellow in colour. The eggs have a thin, tough shell and are ribbed. These ribs are called reticulations. They have a tiny pit called the micropyle which marks the place the sperm has entered the egg. Air and water enter the egg through the micropyle while the egg develops.
There is yolk inside each egg, which nourishes the larva while it develops. Once the larva is ready, it gnaws through the shell of the egg and emerges as a caterpillar who eats its egg as its first meal. The caterpillar’s job is simple. It eats. And eats. And eats. It constantly eats and grows at an astounding rate. This stage can last from two weeks to about a month. Their diet is pretty limited. Normally they will eat only the leaves of the plant that their mother carefully chose for them. Some are carnivores too; for example, the larvae of the harvester butterfly eat only
As caterpillars grow, their exoskeleton becomes too tight for them, so they moult (lose their exoskeleton). After moulting, while their skin is still soft, they swallow a lot of air so that their bodies expand. After their new skin hardens, they let the air out, so they now have a place to grow on the insides. Typically a caterpillar will moult four to five times.
When their growth is done, their phenomenal appetites sated, the larva stops eating and prepares to pupate. It will empty its digestive system and leave a small dark spot. Then it looks for a safe sheltered place to turn into a pupa.
Once it has found the place, it attaches itself with a silken girdle around its abdomen and a silken pad and cremaster (a hook or a set of hooks) at the hind part of its abdomen. It then splits open, loses its exoskeleton and becomes a pupa. This is the stage in the butterfly’s life cycle when it is encased in a chrysalis and undergoes metamorphosis. It doesn’t eat anything during this time. This stage can last for a few weeks to overwinter. In many species, about a day before the adult butterfly is ready to emerge, the chrysalis becomes transparent.