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Brimstone caterpillar.JPG

Early stages of
butterflies' lives

A Brimstone caterpillar with recently shed skin

Eggs, caterpillars and chrysalides

by Doug Goddard

The metamorphosis of the butterfly through the egg (ovum), caterpillar (larva) and chrysalis (pupa) to emerge as the adult insect (imago) is one of the wonders of the natural history world. Only a small percentage of the early stages survive to adulthood, falling victim to various parasites and predatory birds and small mammals. Searching for these early stages requires a knowledge of the larval foodplants and specific requirements of each species and no small amount of patience and perseverance, but when successful it can be very rewarding.

The egg

Butterfly eggs are very small, usually less than 1 mm in their longest dimension. Shapes, colours and sizes vary with the species, but each has a hard outer shell through which the caterpillar emerges when fully developed, sometimes being eaten as its first meal. Some species lay eggs in batches, but most lay singly. Each species chooses a specific foodplant on which to lay, though some have several choices. A female will investigate the plant beforehand to determine whether it is in the right condition and location, and providing the necessary nutrients, using receptors on her legs and antennae.

The egg of the Dingy Skipper is laid on Bird’s-foot Trefoil, often close to an area of bare ground, growing over a stone or a divot created by cattle grazing. White when first laid, it soon turns orange so that it stands out on the leaf of the plant

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Egg of Grizzled Skipper

The egg of the Purple Emperor is laid on the upper side of a leaf of a sallow at various heights, but always where the leaf is sheltered from the midday sun, as extreme heat will desiccate it. This is a newly laid example. After a few days a darker band develops around the base of the egg.

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The Wood White's distinctively shaped egg

Brimstone eggs are relatively easy to find on Buckthorn bushes in the spring by looking on the outer clumps of leaves, where several may be found together. Planting of a Buckthorn in gardens will attract this species to breed there.

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Dingy Skipper with orange-coloured egg

The Grizzled Skipper chooses Wild Strawberry, Agrimony or Creeping Cinquefoil (shown here) on which to lay the tiny egg, often where the plant again overhangs a large stone or a bare hollow in the ground.

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Newly laid egg of Purple Emperor

Following and watching a female Wood White carefully as she flutters along a woodland ride will eventually be rewarded as she deposits her bottle-shaped eggs on the leaves of Meadow Vetchling on a plant which stands out above the surrounding vegetation. Tufted Vetch and Greater Bird’s-foot Trefoil may also be used.

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Group of Brimstone eggs

The Speckled Wood may be seen egg-laying on grasses along woodland rides and hedgerows and the white globe-shaped eggs stand out on the surface of a blade of grass if one is inspected after a female has settled on it.

The globular eggs of the Speckled Wood


During the next stage of its life cycle the caterpillar changes its skin several times, the number of changed varying from species to species. Each interval between skin changes is called an instar. Most shown here are fully grown in their final instar. Details of the differing appearance of successive instars of each species can be found in Life Cycles of British and Irish Butterflies by Peter Eeles (Pisces Publications 2019) or the UK Butterflies website

Some caterpillars are very easy to find as they are found in large groups after hatching from a large batch of eggs laid together. Examples are those of the Small Tortoiseshell and the Peacock which may be seen on large clumps of nettles almost anywhere in the forest. The Small Tortoiseshell’s are lighter in colour than the very black-looking Peacock’s. The Small Tortoiseshell has two, sometimes three, broods a year, the Peacock usually only one.

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Small Tortoiseshell caterpillars

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A mass of Peacock caterpillars

The most common colour of a caterpillar is green, and the different ones have evolved various strategies to merge in with their surroundings and avoid being detected by predators.

The skippers will use silk to draw the sides of a grass stem together to create a tube within which they feed without being seen. Here the caterpillar of the Large Skipper can be seen in the feeding tube which it has created. 

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Large Skipper caterpillar

A Brimstone caterpillar blends in perfectly with its surroundings as it  lies along the midrib of a Buckthorn leaf and feeds on the edges from there. When at rest it will also raise its front half to break up its outline.


The slug-like Green Hairstreak caterpillar possesses subtle markings and indentations along its surface to enable it to blend in with the foliage of Bird’s-foot Trefoil on which it may be found when fully grown

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Look hard to see the Brimstone caterpillar

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Green Hairstreak caterpillar

One of the most attractive caterpillars when fully grown is that of the White Admiral. It feeds on Honeysuckle amid the shade of the woodland and its spines and shades of green and brown allow it to go undetected, though many are eaten by birds. Feeding from the tip of the Honeysuckle it is well camouflaged.

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White Admiral caterpillar

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White Admiral on Honeysuckle

The Silver-washed Fritillary can be seen in sunny, old clearings in our woodlands where violets grow under the trees. After exploring for suitable violets, a female will fly up to an oak or pine tree and start laying her eggs among the crevices in the bark. Often a layer of moss is chosen in which to deposit the egg. This will hatch after a fortnight and create a layer of silk in which it will spend the winter on the tree trunk. In the spring it will make its way down to the violets on the forest floor. Possessing a series of spines to deter birds, the caterpillar may be found basking on the violet leaves or among leaf litter.

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Close-up of the egg on mossy bark

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Silver-washed Fritillary egg-laying

Silver-washed Fritillary caterpillar

The Purple Hairstreak spends most of its life in the oak canopy and its eggs are laid among clusters of oak buds where they remain throughout the winter to hatch out in the spring. Several may be found together. The caterpillar will spend its life among the leaves of the sprig of oak where its cryptic markings and shape and colour make it very difficult to see. When fully grown, it will descend to the ground to pupate among leaf litter.

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Purple Hairstreak eggs among oak buds

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Fully grown Purple Hairstreak caterpillar

The Chrysalis

Most species are difficult to find in the chrysalis stage but in the case of the secretive Black Hairstreak it is regarded as the stage of its life during which it may be encountered most easily. The eggs and caterpillars are very difficult to locate but the chrysalis is formed in plain sight on the top of a leaf or alongside a twig on Blackthorn. In appearance it mimics a bird dropping which deters predators.

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The chrysalis of the Black Hairsteak

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