Butterflies are not born as ‘butterflies’. Like all Lepidoptera, butterflies are notable for their unusual life cycle with a larval caterpillar stage, an inactive pupal stage and a spectacular metamorphosis into a familiar and colourful winged adult form. The metamorphosis process takes about 10 – 15 days. Below, we take you through the stages of mating, reproduction and metamorphosis with the final stage being a beautiful adult butterfly.
Unlike many insects, butterflies do not experience a nymph period (a nymph is the immature form of some insects, which undergoes incomplete metamorphosis), but instead go through a pupal stage which lies between the larva and the adult stage (the imago).
Butterflies have a courtship routine whereby they first have to find a suitable, potential partner. The male has to first find out if a female has already been fertilised – already pregnant in human terms. If a female has already been fertilised, she releases a powerful chemical called ‘pheromone’, this tells the male that she is unavailable.
Once a suitable partner has been found, the mating takes place. When a male and female butterfly are ready to mate, they perch on a leaf or other surface and bring the tips of their abdomens together. The pair may remain in this position for up to several hours while the male passes to the female a spermatophore, a package containing nutrients and male cells, or sperm, that will fertilise the females eggs.
Both female and male butterflies do not fly while they are coupled.
When the mating has finished, a process occurs which results in the fertilisation of the females eggs. Then she is ready to lay eggs.
Stage 1. Butterfly beginning
The adult female butterfly lays an egg.
Butterfly eggs consist of a hard-ridged outer layer of shell, called the ‘chorion’. This is lined with a thin coating of wax which prevents the egg from drying out before the larvae has had time to fully develop. Each egg contains a number of tiny funnel-shaped openings at one end, called ‘micropyles’.
The purpose of these holes is to allow sperm to enter and fertilize the egg. Butterfly eggs vary greatly in size between species, but they are all either round or oval.
Butterfly eggs are fixed to a leaf with a special glue which hardens quickly. As it hardens it contracts, deforming the shape of the egg.
Eggs are usually laid on plants. Each species of butterfly has its own host plant range and while some species of butterfly are restricted to just one species of plant, others use a range of plant species, often including members of a common family.
The egg stage lasts a few weeks in most butterflies but eggs laid close to winter, especially in temperate regions, go through a diapause stage and the hatching may take place only in spring. Other butterflies may lay their eggs in the spring and have them hatch in the summer. These butterflies are usually northern species including the Mourning cloak Butterfly and the Tortoiseshell Butterfly.
Stage 2. Caterpillar Hatching
The egg hatches into caterpillar (larvae). The caterpillar eats leaves and flowers constantly using its strong mandibles (jaws). It will start its eating process by eating its own eggshell.
The caterpillar molts and loses its old skin many times as it grows. The caterpillar will increase in size several thousand times before pupating (becoming a chrysalis).
Although most caterpillars are herbivorous, a few species are entomophagous (insect eating). Some larvae, especially those of the Lycaenidae (second largest family of butterflies) form mutual associations (a biological interaction between individuals of two different species) with ants. They communicate with the ants using vibrations that are transmitted through the substrate as well as using chemical signals. The ants provide some degree of protection to these larvae and they in turn gather honeydew secretions.
Caterpillars mature through a series of stages, called instars. Near the end of each instar, the larvae undergoes a process called apolysis (the separation of the cuticula from the epidermis in arthropods and related groups). At the end of each instar, the larvae moults the old cuticle and the new cuticle rapidly hardens and pigments. Development of butterfly wing patterns begins by the last larval instar. Wings are very tiny until this stage. Near pupation, the wings are forced outside the epidermis. Although the wings are initially quite flexible and fragile, by the time the pupa breaks free of the larval cuticle they have adhered tightly to the outer cuticle of the pupa. Within hours, the wings form a cuticle so hard and well-joined to the body that pupae can be picked up and handled without damage to the wings.
Butterfly caterpillars have three pairs of true legs from the thoracic segments and up to 6 pairs of prolegs (fleshy, stubby little structures) arising from the abdominal segments. These prolegs have rings of tiny hooks called crochets that help them grip the substrate.
Some caterpillars have the ability to inflate parts of their head to appear snake-like. Many have false eye-spots to enhance this effect. Some caterpillars have special structures called osmeteria (a fleshy organ found in the prothoracic segment of larvae) which are everted to produce smelly chemicals which are used in defense.
Stage 3. Chrysalis (Pupal) Stage
The caterpillar forms into the Chrysalis or Pupae. It takes several hours for the caterpillar to form the complete chrysalis.
Once it has turned into the chrysalis, it will rest. This is known as the ‘resting time’. It will remain in this chrysalis for roughly two weeks, with the exact length of time depending on the air temperature.
The chrysalis is usually incapable of movement, although some species can rapidly move the abdominal segments or produce sounds to scare potential predators.
Stage 4. Adult (Imago) Butterfly
The Chrysalis matures and the butterfly breaks free. After it emerges from its pupal stage, a butterfly cannot fly until the wings are unfolded.
A newly-emerged butterfly needs to spend some time inflating its wings with blood and letting them dry, during which time it is extremely vulnerable to predators.
Some butterflies wings may take up to 3 hours to dry while others take about 1 hour. Most butterflies will excrete excess dye after hatching. This fluid may be white, red, orange, or in rare cases, blue. The butterfly must hang upside for a while until its wings have expanded fully and they are strong enough for it to fly.
The adult butterfly will then carry on the cycle.