Butterflies in Dorset
Colin Varndell takes a close look at some of our county's most beautiful creatures
Published in May ’14
We may all be familiar with common butterflies like small tortoiseshell, red admiral, large and small white (the latter collectively known as cabbage whites), but there are many others breeding in Dorset. Some require very specific habitat conditions, and several species can only be seen on the wing for very short periods of time each year. It seems unfair that beautiful creatures such as marsh fritillary butterflies are only on the wing for a few short weeks in May, while bothersome insects like horseflies can be present from May until September.
Butterflies are generally considered to be indicator species; if a site supports a healthy butterfly population, then the habitat is probably ideal for other species of flora and fauna too. Some of the best habitats supporting butterfly populations include chalk downland, hedgerows, woodland edge, the coast and areas of rough or uncultivated ground where suitable wild food-plants occur. Many of the mobile or nomadic species are attracted to gardens, where they find cultivated plants like buddleia, sedum, marjoram, verbena, rudbeckia and Michaelmas daisy.
Butterfly species in Dorset vary between those that are sedentary – and so tied to specific habitats – and those that are highly mobile and can occur almost anywhere. There is little obvious evidence of the presence of butterflies in winter as they become inactive in order to survive the cold, but they do so in a wide variety of ways. The chalkhill blue spends the winter nestled deep in the herbage as an egg, while the Lulworth skipper survives the cold season as a larva. The orange tip waits out the winter as a pupa – ready to hatch in the first warm days of spring – while the brimstone remains hidden amongst leaves as an adult; it is therefore usually the first butterfly we notice early in the year. Some butterflies cannot survive Dorset winters in any form, and those like the red admiral and painted lady migrate here in early summer from southern Europe or North Africa to breed. There are some records of red admirals There are around 45 species of butterfly breeding in Dorset annually, but this number can fluctuate slightly from year to year. All of our butterfly species also occur in mainland Europe and originated from there. Those of our resident species gradually migrated northwards after the last ice age receded and temperatures rose. Many are at the northern limit of their range, though, and can be adversely affected by habitat deterioration or extreme inclement weather. The fragility of some species is so precarious that only very small changes in local conditions could cause them to vanish from a site.
One of the main problems when a species is lost from a specific location is that even when ideal conditions or the breeding habitat for that species is fully restored it may still take many years for the site to be re-colonised. This is because the colonies of sedentary species are so fragmented across the county. In some cases when species have become extinct at a site in Dorset, re-colonisation has not occurred at all; the dark green fritillary disappeared from Powerstock Common during the 1980s and although this reserve has been greatly improved for butterflies, and despite there being relatively healthy populations of this species elsewhere in the county, it has not returned. The two heathland specialists – the grayling and silver-studded blue – will not venture away from the heaths. Although there is a sub-species of the latter in some of Portland’s quarries.
Some areas of Dorset are particularly good for observing a wide range of species. Bindon Hill for example is a great place to find blues, skippers and wall browns in mid-summer. Fontmell Down in north Dorset supports a wide range of butterflies including the uncommon silver-spotted skipper. As a rule, most butterfly sites are also good for more than one species as well as other wildlife.
The Duke of Burgundy fritillary caused entomologists some concern after it was seen to decline at a number of its former Dorset strongholds, including Powerstock Common. Incidentally, other species which have also gone from this site include pearl bordered and small-pearl bordered fritillaries. However, there is some good news at Powerstock because this is the only place in the county for reliable sightings of wood whites. The Duke of Burgundy does seem to be showing signs of recovering though in some places. Cerne Giant hill is one site at which the Duke has shown an increase in population over the last couple of years.
Several of the county’s nature reserves are managed primarily with the habitat requirements of butterflies in mind. However, the nature reserve network is largely fragmented and represents only a series of small oases. In Dorset, Butterfly Conservation manages several excellent reserves including Lankham Bottom near Cattistock, Alner’s Gorse near Hazelbury Bryan and in two quarries on Portland – Broadcroft and Perryfields. The organisation was formed by a small group of dedicated entomologists in 1968, following the dramatic decline of many of our butterflies. It now has over 19,000 members and, while the work of Butterfly Conservation is nationwide, it is headquartered here in Dorset, so the county’s butterfly populations are being carefully monitored.
As well as being beautiful to behold, butterflies and moths are especially vulnerable to habitat change, which makes them important indicators of the health of Dorset’s wild places, so we should feel doubly uplifted when we see them – not just for the beauty of their patterned colours, but also as their mere presence signals the rude health of the countryside. ◗
❱ To find out more about the work of Butterfly Conservation in Dorset go to www.dorsetbutterflies.com