Butterfly Life Cycle

The life-cycle of a butterfly (and moth for that matter) is a remarkable series of changes between seemingly very different forms culminating in the emergence of a butterfly. Throughout nature there are fantastic and fascinating occurrences of many kinds. The metamorphosis of an egg to a butterfly is just one of those wonders.

The story starts with a pair of butterflies mating. This enables the females eggs to be fertilised. Like many other species in nature there is often a courtship routine preceding the actual mating. Some butterflies fly in spirals, sometimes the female lies with her wings in a certain position.

The Egg or Ovum

The shape of butterfly eggs is remarkably variable. The examples below show some recurring forms but there are many others, for example swallowtail eggs are smooth and spherical. There is some consistency of shape between closely related species. The egg consists of an outer casing, or chorion, inside which is the females fertilised ovum. There is always a minute opening, the micropyle, which is visible as a small pit at the top of some eggs. This structure allows the male sperm to fertilise the egg and probably allows the developing embryo to breathe.

Through her legs the female butterfly can 'taste' plants by a chemical process and so recognise the species, or groups of species which her young will need to feed on. Some butterflies (termed monophagous) only use a single species of plant for their larvae, while others (oligophagous) will use hostplants of similar species and there are some (polyphagous) which will use hostplants from different genera. Once a suitable site is found egg-laying, oviposition, can take place.

Sometimes eggs are laid singly, at other times they may be in bunches, Araschnia levana, lays its eggs in vertical columns. All these tactics have their benefits in terms of survival, a parasite may miss one or two eggs in a large group and similarly may miss one or two widely scattered eggs. Usually the eggs are laid on the foodplant, but some species lay nearby. The Silver-washed fritillary, Argynnis paphia, lays its eggs on the trunk of a tree near to a growth of its foodplant, Viola. Butterfly eggs are attacked by various parasitic wasps so as much as possible must be done to safeguard them.

The eggs take a variable amount of time to hatch, indeed some butterflies remain as eggs through the winter, only hatching when the warmth of spring arrives. I guess they are less likely to be eaten when very small and easy to miss. Usually it takes about 10 days for an egg to hatch. There is an easy exit for the tiny first instar caterpillar to escape from the confines of its egg.

A number of young larvae actually eat their egg shell. For some it is the fuel for their journey to find the foodplant and for others it is the only meal they have before the winter, without it they don't survive.

The Caterpillar or Larva

A caterpillar is an eating machine. Its consists of a pair of jaws or mandibles for chewing plant matter followed by a long gut for digestion. It moves using three pairs of true legs (like all insects) and five further pairs of 'prolegs', sucker like structures with hooks on the end for gripping hold of the leaves and stems. Along the side of the larva are small openings, spiracles, nine pairs in all, through which respiration occurs. A modified set of salivary glands, spinnerets, produce silk. All butterfly larvae are hairy, some quite spectacularly covered with bushes of setae, they may well be off-putting to potential predators.

When first hatched the larva or caterpillar is very small indeed, just a few millimeters long. These first instar larvae look similar regardless of which species they belong to. Usually the caterpillar immediately searches out food and starts to eat, although some species overwinter at this stage.

Due to the nature of the skeleton of insects they cannot grow in the same way that we do. Every so often the caterpillar sheds its skin so that it can expand and grow to a larger size. This process is known as ecdysis and each time it happens the caterpillar moves on to a new instar. Most European species molt four times and so their final stage is usually the fifth instar.

Caterpillars feed for a large part of their time, consuming an ever increasing amount of foodplant as they get rapidly larger. Some species prefer the cover of night to avoid unwanted attention, the Comma, Polygonia c-album, spends most of its time underneath leaves for the same reason. Their excrement, usually called frass, is dropped all over the place in small lumps.

Caterpillars produce a silken thread from organs beside their jaws. This is used for a variety of purposes. It gives the caterpillars a good hold on their foodplant and some use it to rest between bouts of feeding.

When a caterpillar is fully grown it takes time to wander in search of a suitable pupation site. This stage is sometimes known as the prepupa. The larva will let all frass clear its system before pupation.

The Chrysalis or Pupa

The word chrysalis is derived from the Greek work crusoz meaning gold, referring to the colour of some Nymphalid pupae, whereas pupa is the scientific word describing this stage of a butterflies life.

Most of the adult body parts can be seen in the pupa (See image)

Once the caterpillar has transformed into a pupa a remarkable process occurs transforming the contents of the pupa into an adult butterfly. This can take as little as two weeks, but some species over-winter (hibernate) in this stage, only hatching in the warmth of spring. As the pupa is unable to avoid any potential predators they tend to be quite well camouflaged, indeed some are form under the ground.

The pupa hangs onto the silken pad using its cremaster, rather than the anal claspers of the caterpillar. Just before the adult butterfly hatches the pupal skin becomes transparent and the wing pattern is visible inside.

source and image : www.butterfly-guide.co.uk

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