IS ESSEX A POOR COUNTY FOR BUTTERFLIES?
by David Corke
Introduction
"Any keen young student of butterflies would do well to take my advice and live almost anywhere in the
south or centre of England rather than Essex" (Wykes, 1979; writing of the early years of this century).
That Essex has always been a relatively poor county for butterflies is borne out by earlier writers such
as E. Doubleday (1836) and Burrell (1837). That the variety and abundance of butterflies is now
much less than it was in the 1940s and J 950s is undoubted - but the first question in this chapter is "Why
should Essex have long been a rather poor place for butterflies?"
Joe Firmin, in the previous chapter, has reviewed the changing status of Essex butterflies in tax-
onomic sequence. There are many views on the reasons behind the decline of many butterfly species
and here I present some which are alternatives to those expressed by Firmin. I have grouped the species
in terms of the general pattern of their population fluctuations and ecology - rather than the taxonomic
sequence used in the systematic list. I am using only the familiar English names in this chapter; the full
scientific names are given in the systematic list.
Heath, Pollard and Thomas (1984) give an excellent summary of researches into the changing
butterfly population of Britain. They point out that many of the long-term changes (especially those
before the recent extreme agricultural intensification) can be correlated with changing climatic pat-
terns. A run of sunnier summers may well explain the spread of many butterflies in southern England
(Essex included) in the 1940s and 1950s - producing, in Essex, an abundance and variety of species
against which the present impoverished fauna seems even worse than it would if compared with that of
early Victorian times.
Climate is clearly not the only factor involved in determining the spread or restriction of a butterfly's
range. As Heath et al. point out, many of the British species occur in Europe in areas of widely differing
climates. Indeed, some of the best butterfly regions seem to those with a continental climate of hot
summers and cold winters. In Britain, the central south-coast has the widest variety of species - and
quite 'continental' summers. Essex has one of the most 'continental' type climates in Britain - and yet it
is poor for butterflies!
A study of the map of the number of butterfly species found in each 10km square of Britain (Heath et
al. page 139) confirms that Essex is the worst part of south-east England for butterflies: some squares
have less than 10 species and few have over 30. The parts of England with 40 species are the chalk and
limestone downlands: areas where the localised downland species are added to the more widespread
species to produce the high totals. In Essex, downland is virtually absent - only in the extreme north-
west are there some low chalk-hills, but these were converted to arable land by the middle of the last
century and have long been unsuitable for butterflies that need downland turf habitats (Corke,
1984).
Even away from downlands, 'good' butterfly habitats tend to be on sloping ground where hollows or
south facing slopes create sun-traps. The generally flat geography of Essex is another factor making it
poor for butterflies. It is noticeable that some of the best remaining butterfly haunts in the county are
artificial hollows or sheltered sun-traps - namely the railway cuttings (often on abandoned railway
lines) and wide sunny rides in Forestry Commission managed woodlands.
There are two points which should be borne in mind when trying to get a picture of a species status
from the distribution maps. First, the old records (open symbols) represent records from a very long
time period whereas the recent records are from a little over one decade. This may give a false
appearance of recent decline if the species fluctuates in range and abundance. Conversely, a false pic-
ture of wide range and abundance can result from the fact that a whole 10km square is filled with a solid
symbol if only a single butterfly was seen there in a single year since 1970! Species lost to the county as
breeding insects may still have a lot of 'recent' records representing vagrant adults or breeding popula-
tions lost since 1970. The map of the white admiral illustrates this point well; it is far from obvious that
the species may survive as a breeding population in just one group of Essex woods in the extreme north-
east of the county. The map shows nine recent records scattered across the county.
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