For many species the cycle takes a year to complete but others develop more rapidly leading to two or more generations of adults appearing each year.  All species are dormant in the cold of a British winter but different species spend the winter at different stages of development.  (The Speckled Wood alone is an exception and can spend the winter as either a caterpillar or chrysalis.)  This and the fact that the length of time at each stage varies from species to species means that different species are seen as adults at different periods of the year.

Once an egg hatches, the caterpillar feeds on leaves, usually of only one, or a limited range of, plant(s) characteristic of the species.  This means that the eggs must be laid on or very close to this essential plant.  References to the “foodplant(s)” of a species refer to this plant(s) on which the caterpillars feed, not to the plants from which the adults take nectar.

When the caterpillar is mature, it creates a sheath and forms a chrysalis within which the almost magical process of metamorphosis into the adult butterfly takes place.

Butterfly eggs are tiny, no bigger than a pin-head, and are hard to find.

Caterpillars are generally easier to see, though some are well camouflaged.  Sometimes many hatch and live together and those of species such as the Large White, commonly called the Cabbage White, can be a significant pest.  Many of the large caterpillars seen regularly are moth species not butterflies.

Chrysalises are immobile and usually well hidden.

It is the final adult stage of the mature butterfly that we are all familiar with.  Many are brightly coloured and hard to miss as they fly and feed at low levels but a few such as Purple Hairstreaks and Purple Emperors live in the tree-tops and rarely descend to the ground.  Some of the smaller butterflies live for no more than 10 days; at the other extreme, Peacocks and Brimstones may live for up to 10 months.

Adult butterflies have two objectives – to feed and to breed.  Males are often brighter coloured and more active than females so are more often seen.  They will often patrol an area looking for females and may attempt to chase away other intruding males.  Females will often be seen searching for suitable places to lay their eggs.

Adult butterflies sustain themselves by drinking nectar or, in a few species, honeydew, which is secreted by aphids onto the surface of leaves.  They cannot eat anything solid.  Most species will take nectar from a variety of flowers – brambles and thistles are among the favourites for many, particularly in the Wood.  Garden plants such as Buddleia and Sedum also attract several species.

Butterflies are very dependent on sunlight to maintain their body-temperature at a level which allows flight and feeding so are most active between mid-morning and late-afternoon and rarely fly if the air-temperature is below 13oC.  In cool or wet weather they will close their wings and hide in vegetation, often under leaves.

Some butterflies live in discrete colonies, often determined by availability of the foodplant – see above.  Some are weak flyers, only venturing a few hundred yards, meaning that there is limited opportunity for exchange of insects, and hence genes, between the colonies if they are too far apart.  Widespread foodplant availability is thus essential to maintenance of healthy populations and loss of suitable habitat has led to big declines in some species over the last 50-100 years.

Other species live at low densities over wider areas.  Some are powerful flyers and Red Admirals, Painted Ladies and Clouded Yellows regularly migrate to and from continental Europe.

Butterflies are vulnerable to predation at all stages of their life-cycle and only a small proportion of the eggs laid will produce adults.  Birds are major predators of both caterpillars and adults.  The large eye-markings on the wings of some species are thought to be an attempt to divert attacks from more vital parts of the body.  It is quite common to see butterflies with triangular peck-marks from birds’ beaks in their wings.  Dragonflies and some species of bat also take their toll.