Understanding the requirements of British species to create butterfly-friendly arboricultural environments.
BUTTERFLIES on the wing are regarded as a summer tradition, but early spring is also prime time for butterflies, depending on the life cycle of a species.
Like birds, butterflies rely mainly on external heat sources to maintain body temperature and activity. As such, many species are adept at raising body temperatures to levels over and above that of the ambient air by basking in sunshine or by shivering (vibration of flight muscles), two familiar aspects of butterfly behaviour. However, when the temperature of the surroundings drops below a threshold most species are forced into inactivity. As such, low winter temperatures in cool temperate climates like our own clearly threaten survival.
Most species of butterfly have evolved ways of circumventing this problem by entering a dormant, inactive phase. This can be at the egg, larva, pupa or imago (adult butterfly) stage. Those which overwinter at the adult stage are logically seen earlier in spring. The majority of British butterflies overwinter in the larval stage, followed by pupa, egg and adult in that order. A select few can overwinter in more than one stage, like the speckled wood butterfly which hibernates as larva or pupa.
Butterflies which hibernate as adults are the first out and about when the weather warms, which can be as early as February. Species overwintering as adults include brimstone, comma, peacock and small tortoiseshell butterflies.
So, how does all of this fit in with the wooded environment, whether natural woodland or the man-made amenity environments including commons, parklands and golf courses? Essential pre-requirements for butterflies on the wing are sheltering sites during winter and sustenance as nectar for butterflies and food plants for their larvae.
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By understanding the nature of these requirements, the land manager – whether forester, arborist, country park ranger or woodsman – can create environments that are butterfly-friendly. This article considers life cycles, including food and shelter requirements, for a selection of British butterflies which are on the wing in spring.
COMMA (POLYGONIA C-ALBUM)
Polygonia c-album overwinters in the adult stage. Commas are some of the first butterflies on the wing in spring and are subsequently seen throughout most of the year, but most likely absent during the warmth of May and June.
Fulvous was the favoured word used by early lepidopterists to describe the striking background colour of the wing’s upper surface, and though not widely in use today, fulvous (meaning rusty red-orange) is highly appropriate and accurate. Variably marked with black and dark brown, the comma butterfly could conceivably be confused with close relatives like small tortoiseshell butterfly, although its highly scalloped (jagged) wing margins should put paid to that.
That said, some specimens emerging from hibernation in early spring with a rather ragged (rather than jagged) appearance could be mistaken for tatty tortoiseshell butterflies. However, the comma has its own unique signature in the form of a white c-shaped or comma-shaped marking on the underside, almost like a branding and the reason for its name. The wingspan of this medium-size butterfly, and member of the Nymphalidae family, is 55 to 60 mm (male to female).
Cryptic colouration or camouflage provided by the range of browns on the surface of the underwing, together with the jagged wing margins, provides highly effective concealment of the comma. It blends in with the various shades of brown displayed by the dead leaves which comprise woodland leaf litter.
The comma butterfly traditionally overwinters in woodland inside hollow trees or within log piles, so don’t rush to remove those old trees and make sure you leave deadwood in situ. Don’t be tempted to dismantle and take away woodpiles in winter even if you need the firewood because the comma butterfly has an even greater need.
Not a lot is known about exact hibernating sites because so few commas are actually found hibernating in winter. Examples of sites where found include honeysuckle tangles and coppiced hazel. In form and colour, this butterfly would appear too cryptic to find. Mimicking the shape, form and colouration of dead leaves is clearly a clever evolutionary trait for a species that hibernates in broadleaf, deciduous woodland.
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Individuals may become transiently active on warm days in late winter but will finally exit the dormant winter phase during March with nectar sources for energy as top priority. Suitable nectar plants are few and far between at this time of year but early flowering sallow and wild Prunus (wild cherry and blackthorn), ornamental flowering cherry and spring flowering woodland plants including primrose, cowslip, ground ivy, purple dead nettle and dandelion are used. Later flowering plants like bluebell are used in April.
Adult comma butterflies, sufficiently fed and watered, do not travel far to breed with females, laying eggs on suitable larval food plants in open woodland or at the woodland edge in April/May. There are two broods per year, beginning in April/May and July/August.
Larvae are shaped like bird droppings, while the pupa resembles a withered leaf and highly appropriate too as camouflage in woodland environments. The term chrysalis is generally used to describe pupae of all butterflies, although some early authors like Richard South (Butterflies of the British Isles, 1906) say ‘chrysalis’ should be reserved for those special few species with ‘gilded’ pupae (gold and silver markings), of which the comma is one.
I wouldn’t go as far as to describe comma butterfly larvae as polyphagous although they do use a botanically wide range of food plants. Like many other Nymphalid butterflies such as peacock and red admiral, the main larval food plants are members of the nettle family, and especially the common stinging nettle (Urtica dioica). Other food plants include Humulus lupulus (hop), Ulmus (elms), Ribes (currants) and Salix (willow). Prior to hibernation in late autumn, comma butterflies range more widely in search of nectar and rotting fruit, such as blackberries and fallen plums, and are frequently seen in gardens.
Much is made of the ups and downs of British butterflies in relation to weather, climate and land use. However, many species have experienced alternating generous and lean times for centuries with comma as a prime example. Richard South (1906) and W.S. Coleman (British Butterflies, first published in 1860) describe how in 1830 comma was plentiful around London, including Epping Forest and Hertfordshire, and also in south-west England. However, some 70 years later, at the end of the 19th century, the comma was essentially confined to Herefordshire, Worcestershire and Monmouthshire. More than a century later, the comma appears safe, widespread across Southern and Midland regions of England and moving northwards at a healthy pace.
SPECKLED WOOD (PARARGE AEGERIA)
Most British butterflies were named after their wing colouration and markings. Examples are the peacock, after the resemblance of the wing pattern to the tail feathers of its avian namesake, and the comma due to a white comma-like marking on the underside of the wing. The names of other butterflies like gatekeeper clearly describe a favoured habitat.
However, there appears to be some ambivalence in speckled wood, the common name of Pararge aegeria. Speckled woods display dark brown wings, speckled with various shades of buff or light brown and with eyes which are velvety black with a pure white centre spot. However, the species’ favoured habitat is partially shaded woodland illuminated by dappled or speckled sunlight. Individuals are most frequently seen flitting around woodland clearings where their speckled-wing appearance blends in well with the light and shade.
When air temperatures are low in early spring the speckled wood will settle on sunlit leaf litter to soak up the warmth from the dead leaves and generally spend more time stationary than on the wing. It would be interesting to know if they seek out leaf litter from particular tree species on the basis of superior thermal properties or specific aromas.
Documented in James Petiver’s Papilionum Britanniae (1717), apparently based on a specimen seen and captured at Enfield in Middlesex, this butterfly was first called the Enfield Eye. Later that century it was renamed ‘Wood Argus’ by Benjamin Wilkes due to its multiple wing eyes, after the hundred-eyed monster of Greek mythology. The name speckled wood first appeared in Moses Harris’s famous book The Aurelian, published in 1766. Although whether ‘speckled’ refers to wing markings or light patterns on the woodland foliage is anyone’s guess today.
Speckled wood is common and frequently seen in grassy areas in or around woodland but also in hedgerows, on scrubland, parkland and in gardens. Speckled wood butterflies have brown wings with creamy-yellow spots. There is one black and one white eye spot on the forewing and three on the hindwing. The underwing surfaces are coloured orange, yellow and brown. However, colouration is complicated by regional and seasonal differences.
The appearance of the speckled wood changes from north to south in the British Isles to form a so-called ‘cline’ or geographic gradient. Butterflies in the north are dark brown with white spots while those found in more southerly locations are dark brown with orange spots.
Go back two centuries and UK lepidopterists refer to a similar colour/pattern phenomenon, although the geography appears to have changed. They talk about a ‘true’ southern form of south-west Europe and North Africa called ‘egeria’ and a northern form (egerides) of Central and Northern Europe including the entire British Isles.
Yet another oddity unique amongst British resident butterfly species is the ability of the speckled wood to overwinter as either a larva or pupa, which leads to a staggered emergence of adults in spring. Modern texts talk about two or three subsequent generations depending on location and weather conditions, although four generations were reported in the south of Surrey in 1862 by 19th-century lepidopterist Charles Golding Barrett.
The net result is speckled woods on the wing from April to September with a few seen as early as March, and as late as October, especially in the south of England. The staggered spring start is clearly of benefit, allowing the species to come back if spring weather conditions are very wet and cold.
Indeed, the speckled wood butterfly is riddled with oddities including the preference of adults to nectar on aphid honeydew in the tree canopy rather than flowers in the understorey or on the woodland floor. Flowers only tend to be used as sources of nectar at the beginning and end of the season when aphid honeydew is in short supply. Speckled woods are more likely to be seen fluttering upwards in a ray of sunlight or basking on sunlit leaf litter than drinking nectar of flowers.
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The reason why speckled wood butterflies frequent grassy areas is that females lay their white eggs on a range of native grass species, including Yorkshire fog, cocksfoot, common couch grass and various meadow grasses (Poa species), which are the food plants for hatching larvae. Hatching caterpillars (larvae), which are bright green with darker green- and cream-coloured stripes, go on to form a pupae in varying shades of green which hang from stems.
Butterfly conservation describes the speckled wood as one of few recent success stories for British butterflies. Surveys show a 71 per cent increase in distribution (south to north) and an 84 per cent increase in frequency over the last four decades, which they ascribe to a changing UK climate.
RED ADMIRAL (VANESSA ATALANTA)
One striking memory from late summer in the 1950s is the Buddleia bushes in my aunt’s garden being covered with butterflies, specifically red admirals, which once seen are rarely forgotten. Red admiral ranks in the topmost group of most beautiful British butterflies, but how British is the red admiral?
Those of the 1950s were almost certainly migrants, having flown into Britain from Europe starting in May and progressing through the summer months, or offspring from these migrants emerging from August through to October. According to some butterfly experts, red admiral has begun to overwinter in southern England, perhaps explaining the increase in number and why red admirals are regularly seen on the wing in March and sometimes earlier. However, residents are considered to make up only a small fraction of the total population. Most will succumb to British winter conditions, especially outside of southern England.
As a frequent visitor to gardens, red admiral is one of our better-known butterflies, unmistakable with its velvety black wings intersected by bright, scarlet bands. There is a touch of the exotic about the red admiral and, for me, this evokes memories of the butterflies which flitted effortlessly from flower to flower in the near 100 per cent humidity of cocoa plantations.
Migrants start to arrive in May and June with the next generation of adults swelling numbers from August onwards. Red admirals indulge in a wide range of nectar sources. Hawthorn and blackthorn blossom are used early in the season with Buddleia, bramble and thistles among those used to source nectar later in summer. Ivy blossom used in September and October is clearly an important supply of nectar for this late-season flying butterfly.
Like the comma butterfly, the red admiral is partial to rotting fruit and especially sugar-rich plum windfalls from the trees. A special sweet and sugary tipple rarely mentioned in modern texts but described in detail over a century ago is birch tree sap. South (1906) described how a tree stem bored by goat moth larvae (Cossus cossus) will be visited by nearly every red admiral in the vicinity. One observer saw some 30 red admirals gathered around a wounded birch tree on Wimbledon Common.
Oviposition is a deliberate affair with female butterflies changing from their usual powerful movement to a slow and steady flight mode, flitting from leaf to leaf of the food plants to oviposit on suitable leaves. Multiple eggs, light green at first but darkening with maturity, are laid amongst one patch of nettles with larvae variable in colour taking about one week to hatch. Pupa like that of the comma is gilded, being prettily ornamented with gold along the centre of the back and on the thorax and head, thus qualifying, according to South (1906), as a chrysalis.
As for many other Nyphalid butterflies, including comma and peacock, members of the nettle family (Urticaceae) are the preferred plants for oviposition and as food plants for red admiral butterfly larvae. Common stinging nettle (Urtica dioica) is the main food plant, although hop (Humulus lupulus), pellitory of the wall (Parietaria judaica) and small nettle (Urtica urens) are also used.
Larvae grow and develop within tents which they form by folding the margins of a leaf together with the insect only venturing outside to feed. New tents are created as the larva grows to leave a number of larval leaf-tents on a single patch of nettles. Such behaviour makes red admiral larva one of the easiest to see and locate. Larvae are invariably found in the largest of these tents. They occur in a range of colour forms from black, greenish-brown to pale, yellowish-green and pupate after 3–4 weeks depending on temperature. For metamorphosis of the larva into a pupa, a more intricate tent is created, formed from several leaves pulled together with silk.
NOT TOO TIDY PLEASE
The clear message for those looking to encourage and nurture butterflies is don’t overdo the tidying up, whether dead wood such as tree stumps and wood piles or herbaceous plants like stinging nettles and creeping thistles, generally regarded as invasive weeds despite being native species. Even those perennial weeds including dandelion and red dead nettle, which invade the soil around amenity trees, but are already in flower by February, provide nectar for butterflies on the wing in early spring.
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