Woodland Glade Butterflies
Although large and often vividly coloured, some woodland butterflies can be difficult to spot among the trees in which they live, but late summer, and even the rotting fruits of autumn, may attract them down to feed.
An ideal butterfly wood is one with a mixture of open glades and mature trees, interspersed with sunny rides. Our ancient woods were of this type, with sunny glades and luxuriant undergrowth, and dominated by oak-a tree seldom planted today because it thrives only on deep, rich soils.
However, our current practice of planting woodland remnants with economically sensible. But alien, conifers is accelerating the loss of ancient woodland. Once the conifers have matured, the number of butterfly species to be found in these woods fall dramatically.
Although at least 20 of our native butterflies are associated with woodlands, four species-the purple emperor, white admiral, wood white, and comma-can be considered as true woodland butterflies.
The comma butterfly
This is perhaps the odd one out among the four species as it is frequently found in gardens. It is, however, still considered to be a true woodland species. Females preferring to lay their ribbed eggs on nettles in woodland clearings. Other larval food plants include wych and common elm, hops and redcurrant.
Comma caterpillars resemble bird droppings, having black and white markings, the arrangement and shape of which change at each moult and help them to deceive vertebrate predators. When full-grown, the caterpillar selects a sturdy leaf and spins a pad of silk from which the chrysalis is suspended. This is brown, with small gold specks and blotches, and irregular in shape, like a dead leaf.
Eggs laid in April and May produce a generation of butterflies in July, which may include a number of specimens with pale undersides. This variety is called hutchinsoni, and its colouring is thought to be genetically controlled. When the July brood lays its eggs, the generation of butterflies produced from them in August and September are all normal comma butterflies.
In the autumn, the adults feed on the nectar of thistles and ragwort flowers before they go into hibernation for the winter.
Unique white butterfly
The wood white is unique among British whites in being our only representative of the sub-family Dismorphiinae, an almost exclusively South American group. This delicate white butterfly can be recognised instantly by its slow, bobbing, fluttery flight. Both sexes have a black tip on each forewing, although this is rather paler in the females.
Female wood whites prefer to lay their eggs on vetches and bird’s-foot trefoil in shady woodland rides. The caterpillars are green and blend in perfectly with the colour of their food plants, making them very difficult to find. They mature quickly and form chrysalids on the growing plant, in which they normally overwinter. Thus the wood white may spend up to 10 months of the year as a chrysalis, although in certain years two generations are produced-the normal one in May to June and a further brood in July to August.
Graceful white admiral
Although strikingly black in colour on its upper wings, with white transverse bands, the white admiral is not as conspicuous as one might expect. The contrasting colours break up the outline of the wing, camouflaging it in the dappled light of the woodland.
A graceful butterfly, flying with a strong but elegant gliding motion, it feeds on bramble blossom and honeydew. The females lay eggs singly on wisps of honeysuckle growing in dense woodland.
The first two caterpillar stages feed in a very characteristic way, spinning a pad of silk along the main vein of a leaf and eating either side of this pad, camouflaged by their own droppings mixed with silk. As autumn approaches, the caterpillar forms a tent of leaf tissue called a hibernaculum. Before settling down in it for the winter, it secures the leaf to the honeysuckle stem with silk, so that it does not fall off with the other leaves.
The caterpillar awakes in spring and after a brief spell of feeding it moults to reveal a spectacular, spiny green skin. Eventually, it forms a green and gold chrysalis. Unfortunately, both the large caterpillars and chrysalids are eaten by birds and attacked by parasitoids, and many of them never reach the adult stage.
Majestic purple emperor
One of the earliest species to be recognised in the 17th century, the purple emperor was once known as the Emperor-of Morocco. The wings of the males have a rich purple-blue sheen which can only be seen from certain angles.
Female purple emperors are rarely seen for they spend virtually all their lives at tree-top level, particularly around oak trees. They come down only to lay their eggs singly on the upper side of sallow leaves. Males also spend much of their time in the tree tops, chasing off other males that approach their territory, although they sometimes come down to woodland rides to drink at puddles or feed on carrion or dung.
All four species are linked by a common feature: they have all undergone dramatic changes in distribution over the past century. The best known case is that of the comma butterfly which, after occurring over most of southern England in the late 19th century, became restricted to the Wye valley in the early 1900s. Since then, it has gradually returned to its old localities and is now found as far north as Wales.
The most likely explanation for such fluctuation in numbers is a change in climate in the early part of this century. It appears that, in the early part of the 20th century, summer temperatures were cooler than average and corresponded with a period in which the range of these species contracted. When the weather is cool, caterpillars take longer to grow and are therefore vulnerable to predators for a longer period. Also, adult butterflies are relatively inactive in cool conditions and die before they have laid their full complement of eggs.
After this period of decline in the early 1900s, all four species mentioned above underwent a dramatic increase in numbers. This coincided with a series of warmer-than-average summers in the 1930s. Unhappily, population numbers are now falling again and with the decline of suitable woodland, we can only hope that by the time these species recover and begin to spread again, enough of their habitats will be left to support them.