Aristocrat Butterflies

Proboscis of Peacock Butterfly, Inachis io

Image: Ian Dury

The fermenting juice of rotting windfalls brings many wasps and flies, the odd hornet, and, with luck, butterflies. If nearby there are also September flowers – especially Michaelmas daisies and buddleia blossom – the chance of butterflies is increased still more.

By this time of year the majority of butterflies still on the wing are those that spend the winter as adults, rather than as eggs or larvae or pupae. Typical of this group are certain members of the nymphalids, a family which contains some of the showiest and best-known British butterflies, such as the Peacock, the Red Admiral, the Comma, and the Small Tortoiseshell.

So entranced were the early lepidopterists by this family that they called many of its children the “aristocrats” and gave them names to match. The Purple Emperor, the White Admiral (the word Admiral is a corruption of “Admirable”), the Camberwell Beauty, and the Large Tortoisehell are rare in England today. A frequent cause of a butterfly’s decline is increasing scarcity of the plant or plants on which its caterpillar feeds. In the case of the Large Tortoiseshell, for example, the major food plant is elm, and, through Dutch elm disease, we have lost twenty-five million trees since 1970.

But not all is gloom. Many sorts of insects – a number of aristocrats among them – depend either partly or completely on the nettle for food and shelter. The nettle is highly nutritious for hungry caterpillars and, best of all, avoided by grazing animals. It is usually found in association with man, thrives on waste ground, and may be locally abundant.

The Red Admiral, the Peacock, the Small Tortoiseshell and the Comma are all partial or exclusive nettle-feeders, so it is no surprise that these are the aristocrats commonest today. The Comma – a tawny butterfly with its jagged-edged wings spotted with black – has in fact been increasing its numbers since about 1925, for reasons not fully understood.

The Comma gets its name from a small, comma-shaped mark in silvery white on the underside of each hind wing. The rest of the undersides are camouflaged with brown and darker brown pencillings, so cleverly that when a Comma closes its wings it can seem to disappear. Its caterpillar, which leads a solitary life, goes one better in the camouflage game and looks very much like a bird dropping. The adult butterfly is often seen in gardens, where it may form an attachment to a small area – sometimes of just a few yards square – with its own favourite leaves for resting and basking in the sun.

The Peacock and the Small Tortoiseshell also have drab, disguised underwings which contrast with the ostentatious patterns above. The Small Tortoiseshell, marked with orange, brown, contrasting patches of black and white, and with a tracery of tiny blue half-moons along each trailing edge, is perhaps the most familiar of the garden aristocrats.

The Peacock is almost as common. It is so called from its four large “eyes”, the ones on the hind wings being especially like those on peacock’s feathers. The colouring and texture of its wings are almost unbelievably subtle and complex, more inventive and in far better taste than even the most costly Oriental carpet. However long you study a resting Peacock, always apprehensive that at any moment it will decide to flit away, your eye can never take it all in; the brain can remember no more than the crudest essentials of the pattern.

It is no answer to catch and kill the insect and pin it to a board, for then, with its life, its vibrancy is lost and the colours seem to fade. Butterflies must be admired in their totality, and that includes sunlight and air and the liberty to fly away.

The fruit-strewn turf of a neglected orchard is a fine place to see Red Admirals. Drunk on cider and greedy for more, they are more approachable than usual. The wing-pattern is predominantly black, with a scarlet band across each forewing, another on the trailing edge of each hind wing, all offset by white splashes and touches of azure. As it sips the sweet, intoxicating juice the butterfly continually opens and closes its wings as if in ecstasy. The scene is almost one of decadence. In places two or three Red Admirals jostle with Peacocks and wasps for the best places on the decaying fruit.

This taste for decay is reminiscent of some of the really big tropical butterflies which flock to putrefying carrion. At one time Purple Emperors were baited with dead rabbit; besides rotting fruit, the Red Admiral likes the rich sap oozing from damaged oak trunks.

The Red Admiral, like several other nymphalids worldwide, is a migrant. It arrives in May, having flown here from North Africa or Southern Europe, and lays its eggs, singly, on the upper surface of nettles or related plants. These eggs give rise to the resident summer generation; some of the butterflies feeding in the orchard may be on a return migration, for the Red Admiral is unable to withstand the northern cold and does not hibernate north of the Alps.

The Peacock, the Comma, and the Small Tortoiseshell, though, are able to withstand it, and in the next few weeks will be seeking safe places to hide for the winter. With their wings closed, leaving only the camouflaged undersides showing, they are easily missed by predators. They are also easily missed by humans: when giving the garden shed its autumn turn-out it is worth remembering that some of these butterflies may well have staked their all on a crack or crevice in some dark corner.

There they remain, month after month, motionless and with their body functions almost at a standstill. A few warm days in March are enough to wake them, which is why Peacocks or Small Tortoiseshells are among the first butterflies to be seen in spring. Then there is no rotting fruit to attract them; they must break their fast with a purer nectar sipped from banks of heather or other early blooms.

It might be preferable to think of them at that spring, rather than this autumn, equinox, and, tiptoeing a retreat through the dew-soaked grass, leave the orchard and its inhabitants to their orgy of decay.

(Introduction to these pieces; see all)

Dragonflies

Anax imperator

Image: Agnieszka Urbaniak

The dragonfly is the heraldic emblem of these August afternoons. It is a creature of the heat, its darting activity and purposefulness a direct contrast to the lethargy that overtakes the canal, the river, the weed-choked ponds and streams. Its colouring belongs more to the tropics than to the English lowlands; and in its ferocity the dragonfly reminds us of the merciless insect-war going on, mostly unseen, everywhere in the dense vegetation of summer at its height.

Throughout the whole animal kingdom, indeed, there are no more brilliant colours than those of certain dragonflies. Insect colours are produced in various ways and for various reasons. Some pigments are mere by-products of other bodily processes, with no special significance, but most have some function, however obscure.

The bright yellow laid down in the cuticle of, say, wasps or bees, gives notice that the animal is not to be trifled with. Reds and oranges often signify that the owner is unpleasant to eat. Many other colours and patterns are important in camouflage, courtship, mating, or the defence of territory.

In some insects, colours are produced by intricate structural effects as well as by simple pigments. Iridescence in the more dazzling hues of many butterflies, and the metallic bronzes and greens of beetles, for example, results from an interference effect – involving the reflection of certain wavelengths of light from successive layers in the insect’s scales or cuticle. These colours are brilliant enough, but the dragonflies have gone one stage further.

Besides having a wide complement of pigments, they make use of a phenomenon called Tyndall scattering. In this, light is dispersed in all directions by irregularities in the cuticle surface or by granules laid down just beneath it. The size of the irregularities or granules is minutely adjusted to the wavelength of the light which is to be reflected.

Tyndall scattering is responsible for the incandescent blues and greens of many of our dragonflies. It depends for its success on a dark masking layer below the granules, provided by a brown-violet pigment, an ommochrome.

Ommochromes are widespread in insects. As well as providing brown, red, and yellow body-colours, they have a more specialized use as masking pigments in vision, isolating the individual elements of the compound eyes and enabling them to function.

This leads us to another remarkable feature of the dragonfly’s life, the refinement of its eyesight. Dragonflies are normally day-flying insects. They rely almost entirely on their eyes: the antennae, the seat of taste and smell, are poorly developed. In some insects the compound eyes may contain only a few widely spaced elements; in the dragonfly there may be ten thousand or more in each eye, closely packed together in a hexagonal formation.

Each element in the compound eye sends a signal to the brain, forming a sort of mosaic image. Compared with the human eye, focusing ability and acuity are not very impressive, but the dragonfly’s eye is supremely well adapted to detecting movement. There is very rapid recovery of bleached visual pigments, a high so-called “flicker rate”, enabling the animal to make sense of the landscape as it races past, and enabling it to see and catch its prey with lightning speed.

The prey consists mainly of flying insects, sometimes other dragonflies. It is caught with either the jaws or legs. The legs are found well forward on the thorax, which is itself tilted in such a way that they form a basket to scoop an insect from the air and hold it steady while the mouthparts are brought into action.

There are two sub-orders of dragonflies. The first contains the damsel-flies, and the second the larger, more powerful dragonflies such as the fearsomely named Anax imperator. The eyes in this second group reach an astounding peak of size and development, covering most of the surface of the head.

Much time is expended by the insect in cleaning the eyes with special movements of the forelegs. The head is balanced on a delicate suspension mechanism which allows it to swivel, giving all round vision. So delicate is this mechanism that if the dragonfly hits head-on even a lightweight obstruction – such as the folds of a collector’s net – irreparable damage will be done.

Set beside the technical achievement of constructing just one dragonfly, human efforts to date in the fields of cybernetics and microelectronics look distinctly clumsy. To be fair, the craft of dragonfly-making has had some three hundred million years in which to be perfected: the dragonflies were among the first of the insects to evolve.

The individual adult dragonfly also has a long time in which to develop. Most of a dragonfly’s life is spent underwater, as a nymph, a fierce carnivore which repeatedly moults its skin as it grows in size. There may be a dozen moults in all, and the underwater period varies from one year in the damselflies to a dozen in the largest species. When the time comes for the final moult – usually in June or July – the nymph crawls up a plant-stem, often during the early hours, and, with frequent pauses for rest, breaks out of first one part of the skin and then another.

By dawn the newly emerged, or teneral, dragonfly resembles a mature adult in all respects except for its pale colouring and the flaccidity of its wings and body. As the sun rises the wings harden and become ready for flight. The cuticle hardens also, and within a few hours the insect is ready to fly: the colours develop over a period of days.

In the few weeks of life remaining to it the dragonfly must mate. Females are actively sought out by the males, which frequently are strongly territorial, maintaining one stretch of water as their exclusive property. The eggs are laid in vegetation, or simply scattered in the water to sink to the bottom.

With the first frosts the remaining adults are ruthlessly cut down. Together with hundreds of millions of other insects, they have betrayed themselves by leaving eggs to perpetuate the race. They are no longer required. Thus does Nature treat the most intricate fruits of its creation: and thus vanishes the magical dragonfly, emblem of this brief English summer.

(Introduction to these pieces; see all)

Bumblebees

Image: Andy Potter

Spreading along the base of the house wall is a large and old-established clump of Aubrieta, making a mass of small, purplish-lavender flowers. Because the wall is sheltered and faces south, the flowers always come out early and attract any bees that may be in the vicinity.

At lunchtime, when the sun was especially warm, a bumblebee was clambering from flower to flower, taking nectar and pollen. It was a large bee, a queen, with long, silky and luxuriant fur, black except for the buff collar, belt, and tail. Close inspection revealed that the hairy “pollen baskets” on the hind legs were not being filled. Instead she was feeding directly, as if stoking up after a long winter spent underground.

Although a few individuals of some species break their hibernation as early as February if the weather is mild, most emerge in April or early May. Like the smaller honey-bee, the bumblebee is a social insect and nests in colonies. Unlike the honey-bee, though, no worker bumblebees survive the winter. When she emerges in spring, the queen bumblebee must found a new colony from scratch.

Many of the really common species nest underground. Once she has replenished her reserves of fat, the queen searches for a likely site. Often an old mouse- or vole-nest will be taken over, and the bedding left by the previous occupants is rearranged according to her taste, forming a hollow chamber about the size of a fist, lined with the finest of the nest material.

Insects are cold-blooded, but bumblebees are able to generate heat, both by changes in body chemistry and by a muscular movement rather like shivering. During and just after nest-building, the queen becomes “broody” and her body temperature rises. She may sit in the nest chamber for long periods before the eggs are laid, and her body warmth removes any trace of dampness from the bedding.

Once the chamber is ready, she goes out foraging for nectar, which she brings back in her crop. Some of this is smeared on the inside walls of the chamber, helping to consolidate the nest material, and serving also as an emergency supply of food in the event of bad weather.

The eggs of a bumblebee are white and sausage-shaped and about two millimetres long. They develop in eight tubes which arise from the two ovaries, so that, in some species, only eight eggs are laid at a time; others may lay sixteen.

During her foraging the queen also brings back pollen, which she moulds into a lump in the centre of the chamber. The eggs are laid in this pollen, and then covered with the wax which she secretes from glands in her abdomen. The wax canopy extends to the floor of the chamber, helping to hold the egg-clump in place. The queen sits on top of the clump, using her body-heat to brood it.

Wax is also used to make a special pot for holding a reserve of nectar. The pot is usually placed near the entrance, so that the queen, while she is brooding, can extend her tongue to feed. She faces the entrance as she broods so that she can repel intruders – predators, other queens who may want to take over the nest, or queens of the cuckoo-bumblebees which will destroy her own brood and put another in its place.

The eggs hatch after about five days. The grubs feed on the pollen in the clump, which the queen now replenishes with further foraging trips. She must not spend too long away from the nest at this period, or the temperature of the clump will fall and development of the brood may be retarded. If the temperature drops below 10°C they may even die.

The grubs turn into pupae, spinning papery cocoons for themselves. At this stage the queen scrapes most of the wax from the clump and constructs a new layer or row of cells in which the next batch of eggs is laid.

The pupal stage lasts about a fortnight. About five weeks after the first eggs were laid, the first generation of young bees emerges. These then become the first workers, helping with the care of the later broods. The workers are always females, which are produced as a result of sexual reproduction. The males, or drones, are produced from eggs which are not fertilized. They are born towards the end of the life of the colony, and play no part in foraging or nest-maintenance.

At about this time the new generation of queens is also raised. Queens differ from ordinary females only in the care that they receive in their early stage, being supplied with very much more food than a developing worker.

The males leave the nest almost as soon as they are able to fly, and spend an idyllic, if short, existence, lazing about on flowers, needing to feed only themselves, and engaging in elaborate ceremonial flights designed to attract a mate. When the young queens emerge from the nest, they locate the males at visiting-places which are usually marked by scent and may have been used for the purpose by generations of bees. Most females will mate only once, and then, a supply of sperm stored in their bodies, seek out places in which to spend the winter months.

Meanwhile the workers of the old colony gradually die out – foraging is a dangerous business, with many casualties – and, by the onset of autumn, the queen herself, exhausted after all her efforts, is also dead. The first frosts kill off any stragglers, leaving only the young queens to carry on the species.

And now, after a winter spent in suspended animation, they are groggily emerging, like the queen feeding on the Aubrieta by the wall. Soon she will have to find a nest, and then it will begin all over again.

(Introduction to these pieces; see all)