with plenty of wild-flowers which the adults visit. Before the recent switch to intensive arable and
improved' pasture, these species were common in farm fields. They now survive mainly on roadside
verges, railway banks and the open land near gravel-workings. These habitats are sufficiently wides-
pread that the butterflies are still widespread: although their local density is still as high as before, the
average density across the whole county will be much lower than thirty years ago.
Three of the species that have declined in both range and abundance are also characteristic of
grassland habitats and have larvae that feed on small broad-leaved herbs. These species are the dingy
and grizzled skippers and the brown argus. These have declined much more dramatically than the
distribution maps suggest. Heath et al. have pointed out that in the final stages of extinction a local pop-
ulation declines very rapidly indeed. It seems quite possible that these species may be in their last few
seasons as Essex residents. As well as the loss of suitable grassland to modern farming, the increased
height of grass verges and waste ground, no longer intensively grazed by rabbits, has reduced the abun-
dance of small herbaceous plants in grassland. A similar effect has been caused on roadside verges due
to the replacement of haycutting by mechanical flailing which leaves the cut vegetation in place,
increases the soil fertility, and encourages the fast growing tall plants at the expense of the smaller
herbs.
Only two species whose larvae are grass-feeders have declined dramatically. These are the grayling
and the marbled white. The Victorian records (Fitch, 1891) indicate that both were declining then: but
populations survived in both inland and coastal areas. Inland, marbled whites were found mainly in
moist grasslands and graylings on heaths. Both habitats declined due to agricultural changes. Near the
coast each lingered on, the grayling in heathy and dry grassy areas near Colchester and the marbled
white in the Rochford area. Even the once strong colonies of graylings on the nature reserves at
Fingringhoe and Colne Point disappeared. At Fingringhoe this could well have been due to habitat
changes as the open habitats went through ecological succession to more scrub-dominated areas. This
explanation cannot apply at Colne Point and the disappearance is a mystery. Like the grayling, the
marbled white has been in decline since the 1960s for no very obvious reasons. The long-term survival
of either species must be in serious doubt.
Like the grayling, the green hairstreak is a species of heathland areas. The number of colonies
have declined in recent years although it is still present in several heathy areas where gorse or broom
(the larval foodplants) are abundant.
The white admiral is a woodland species whose recorded fluctuations in Essex are quite similar to
those of the woodland fritillaries described above. The only real difference is that the white admiral
still (just) survives as a resident species. Pollard (1979) explained the 1930s and 1940s national
expansion in range in terms of climatic factors: warm summers shorten the duration of the late
larval and pupal stages thus reducing bird predation. Also, the early stages of abandoned coppice
favour the species — as honeysuckle reaches a stage which is ideal for the larvae (Heath et al).
Localised or rare species with lesser recent changes in abundance
Three features unite the four species that I place in this group: their present status appears little dif-
ferent now from that reported by Fitch (1891). all have larvae that feed on trees and (in marked con-
trast to the majority of extinct or greatly declined species) they do not overwinter in the larval
stage.
The brimstone has always been a firmly established resident which never reaches extremes of
abundance. The larval foodplants (buckthorns) are not universally distributed in Essex (Jermyn,
1974) but the great wandering tendencies of the brimstone (especially by males in spring) has pro-
duced records from a wider area than that in which the species can breed.
The holly blue shows very distinct cycles of abundance, becoming quite common and widespread
every few years. This type of cyclic fluctuation is characteristic of species interacting with a host
specific parasite that increases the proportion of larvae parasitised as the host gets commoner and
vice-versa. The holly blue is host to a distinctive parasitic wasp but the population dynamics have not
been fully investigated (Heath et al).
The white-letter hairstreak has declined since the war but, despite the effects of dutch elm disease
on its larval foodplant, is still quite widespread and found in many of the same areas where Fitch
(1891) noted its presence. As the larvae require flowering elm on which to feed, the possibility of
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