Harewood Forest in early July – butterflies
What a change just over four months makes! Now this ancient woodland is thick with dense foliage and the heavy, humid air thick with the humming and buzzing of insects. Walking through the cool shade of the coppiced hazel to the left the wild gooseberry has scant small fruit, but to the right an occasional, tiny, wild blackcurrant bush can be found. Ahead the sunlight beckons and already the fluttering form of a butterfly, perhaps two, can be seen.
The first is a dark brown Ringlet, a butterfly that loves grassland and, particularly, woodlands with open rides and glades. At first glance, the top surface of the wing has no markings, but if the insect sits and doesn’t move around too much you can just make out two small, dark dots on both the forewings and hind. Sometimes one insect will close its wings and then you may notice that this is one of the few butterflies where the underside of the wing is more visually interesting than the top surface which mere has a smattering of small target-like markings.
Barely have I seen this before a large and dramatic orange flash sweeps in. This is Hampshire’s commonest Fritillary, the Silver-Washed. This butterfly is large, striking, fast flying and ubiquitous in our woods in summer. The larvae feed on the Common Dog’s Violet that grows plentifully on the forest floor beneath the hazel stands, while the adult insects are greedy for sugary, bramble nectar. As with all butterflies, adult life is short, only three to four weeks at most, and this period in their life is all about procreation. One may spot a female flying with a male following in the pheromonal scent trail she is leaving behind her. Just occasionally you may be lucky enough to find a couple in copula, when clearly the female has decided that this male is fit enough to provide her with quality DNA.
About two hundred meters from the start of the trail, on the left, is a clearing where charcoal was made in the 1970s. The local conditions are perfect for butterflies – Ringlets, more Silver-Washed Fritillaries and a flash of yellow from a Brimstone.
At this time of the year it’s a good move to look up towards the top of the oak trees and wait … and wait … and, finally, you should spy a small flash of fluttering silver among the leaves of the high canopy. This is a Purple Hairstreak butterfly. They are rarely seen at ground level because they often spend a great proportion of their lives in the tops of oaks. They are not only the country’s commonest Hairstreak but, surprisingly, the commonest butterfly found in oak woodland. Their eggs are laid on new growth at the top of the oak tree during late summer, hatching the following April. The caterpillar feeds up, mainly on leaf buds and, later, young leaves, before descending to the ground to pupate under moss or general forest floor detritus. The adult butterflies then emerge towards the end of June and fly up to the tree-tops to feed on honeydew, a sugar-rich, sticky fluid secreted by aphids. Adult Purple Hairstreaks may return to ground level on sunny mornings to drink the dew or feed off early bramble flowers.
Aphids, greenflies, are sap feeders. Sharp mouthparts penetrate the phloem tubes that carry sugars, proteins and some minerals around the plant. The insects are especially after the proteins and excrete excess sugars onto the surface of the leaf. It is these foods that maintain many species of adult, woodland butterflies and other insects. Some woodland ants ‘milk’ aphids to release their honeydew and, in exchange, the ants do not eat the aphids!
When looking for butterflies it is best to saunter because, in a good year, the bracken can be alive with Ringlets dancing through it and Silver-Washed Fritillaries swooping above.
Joining the Purple Hairstreaks among the billowing upper leaves of the canopy is a different shaped butterfly. It shows a different flight pattern – a flutter and a glide, is large, dark in colour and almost triangular. At ground level it too seeks out bramble blossom, has almost black wings broken by a line of bold white markings. This is the Prince of the Wood, the White Admiral. Depending on the weather, the adults emerge towards the end of June and lay their eggs on honeysuckle, on which the hatchlings eventually feed. Winter draws in when the caterpillars are still very young and they construct a retreat, by fastening a growing leaf to a twig with silken threads, and then hibernate until spring. If they survive the weather and predators the larvae feed and eventually pupate hanging from the honeysuckle plant.
Butterflies and moths are not without their own predators. Many eggs need to be laid to ensure the species is extant the following year. In a recent local experiment twenty Large White Butterfly larvae were collected, fed in ideal controlled conditions and kept over-winter.
Of the twenty caterpillars only three hatched to adults, another six had been parasitized and hatched small wasps, the remainder died of bacterial infection.
The forest is opening out to the left-hand side. This area was cleared and replanted around ten years ago. The removal of the trees has allowed sunlight to reach what would have been a shadowed forest floor. This opening up has brought in butterfly species which would not normally be considered forest animals. Watch out for Large and Small Skippers.
A butterfly that is present in Harewood, yet seldom seen, is the large and stunningly coloured Purple Emperor. Its larval food plant is willow, particularly Goat Willow / Sallow, but the adults are mostly seen around oaks. The males establish territory and sallying out to challenge other males and hunt for females. Occasionally the adults venture down to feed on bramble blossom and to settle on animal dung, which they probe with their proboscis in search of nutrients. Otherwise they are happy to remain in the upper canopy, sharing honeydew with the Purple Hairstreaks.
Beyond the wild apple tree and blackthorn scrub the canopy opens, so the woodland species are left behind.
A couple of hundred meters ahead part of the formerly ploughed field that reaches up into this valley has been left fallow. It has been colonised by chalk grassland flora and so by different species of butterflies. Here are Meadow Browns and the black and white chequers of Marbled Whites. These latter butterflies are not ‘Whites’ at all, but members of the ‘Brown’ family. Their eggs are scattered over meadows and the hatched caterpillars feed off grasses such as Cock’s Foot, Cat’s Tail and Sheep’s Fescue. This butterfly hibernates through winter as a larva, down amongst the grass roots and leaf litter, waking in late spring to feed, pupate and emerge in early summer.
Living around any brambles are now Gatekeepers, a butterfly of the hedgerows that so often surround chalk grassland. Its caterpillars also feed on grasses. The sexes of the adult butterfly are easily told apart, the forewings of the female being a clear and uninterrupted orange while those of the male have a smudgy spur running across them.
If you are lucky, you may catch a glimpse of something fast and strong, sweeping across the swaying grasses and meadow flowers that stretch down the valley. The flight level and sure. Scattering the Meadow Browns and Marbled Whites as truly lesser mortals, this is the arrogant flight of the Dark Green Fritillary. This large, orange butterfly is very similar to the Silver-Washed Fritillary but whereas the latter love the dappled woods this is a creature of the grasslands. It turns up occasionally in the open spaces in the forest, sometimes forming short-lived colonies, but the nearest site it is known to occupy in numbers is Stockbridge Down.