THE CHANGING STATUS OF ESSEX BUTTERFLIES
by J. Firmin
Since William H. Harwood (1903) wrote his account of the status of Essex butterflies and moths (in
the Victoria County History of Essex) many changes have taken place. Some species which were
widespread or common in Harwood's day have disappeared. Others have become scarce or only
locally common and the overall picture is far from encouraging.
My own studies of Essex butterflies and their habitats stretch back more than 30 years. During
that period the larger fritillaries and the large tortoiseshell have vanished from the woods of Essex
and the white admiral, another beautiful woodland species, has been reduced to a single, precarious
colony in woodland in the north-east corner of the county. In the last 20 years the grayling, once
widespread and locally common on the military authorities' heathland south of Colchester and in
grassy areas on the coast of north Essex, has fallen in numbers to a tiny remnant population on the
outskirts of Colchester.
Before I discuss in detail the causes of the decline in these and other butterfly species it is necessary
to consider the national scene and the climatic and other environmental factors which have affected
and continue to influence the distribution and numbers of British butterflies.
Heath, Pollard and Thomas (1984) point out that over the last 40 years the countryside,
particularly that of lowland Britain, has been radically altered by man's activities. It has always been
subject to change as social and economic factors have altered the nature and intensity of farming
The post-war agricultural revolution, with its use of powerful machines, grant- aided drainage,
pesticides and herbicides, has made a massive impact on wildlife habitats including those sites vital to
butterfly survival. Another highly significant change has been the replacement of deciduous
woodland by quick-growing conifers, a practice which has undoubtedly reduced, and in some cases
wiped out, colonies of woodland butterflies.
Those butterflies which depend on 'unimproved' grassland, with its profusion of native grass
species and flowering plants (for example the common blue, meadow brown, small heath and the
skippers) have all suffered locally serious falls in population as a result of ploughing of pastures and
reseeding of grazing and hay meadows with modern, limited species grass and clover leys.
Heath, Pollard and Thomas (op. cit), when dealing with the pattern of change in butterfly
populations, stress that climate determines the limit of range of many butterflies. Variations in
climate cause short-term fluctuations in abundance and also in range. There is evidence that many
species were adversely affected by the generally low summer temperatures in the latter half of the
19th century. Recent studies of butterfly populations in Britain suggest that they suffer from poor
summer weather in two ways: low temperatures and lack of sunshine during the flight period reduce
the time available for egg-laying; and low temperatures during the late larval and pupal stages
increase the duration of these stages and hence increase the risk of their being taken by predators.
From the 1920s into the 1940s there was a period of warmer than average summers and many of the
species which had declined earlier recovered some lost ground.
Over the last 150 years four British butterflies have become extinct: the large copper (1851);
mazarine blue (1887); black-veined white (1925) and large blue (1979). In the first three instances
they were undoubtedly species on the edge of their European range or, in the case of the large copper,
wiped out by drainage of fens and broads and persecution by avaricious collectors. The large blue
was the victim of West Country habitat and ecological changes and measures to save the surviving
colonies came too late.
Over the same period 18 butterflies have undergone major contractions of range in Britain
including vulnerable downland and woodland species. The picture, however, is not one of unrelieved
gloom. After contractions of range the comma and speckled wood have recolonised former
strongholds and the latter is currently expanding its territory in Essex and into East Anglia.
Because Essex is under so many human pressures, it has suffered more than most counties in the
south-east from the destruction of hedgerows and rough patches of wayside vegetation which sustain
viable populations of butterflies. Fortunately the unrelenting efforts of the Essex Naturalists' Trust
have saved some typical woodland, heathland and freshwater marsh habitats but all too often these
12