This leaves a further seven species which are characteristic of the borrow dykes and
grazing marshes. In some cases the Essex populations are of national significance. Two
species. Aeshna mixta and Orthetrum cancellatum are now widespread in Essex but
appear to be relatively recent colonists. There is some reason to believe that ditches in
the coastal and estuarine marshes were important 'footholds' for the initial colonisation
of both species and both continue to maintain strong breeding populations in the
borrow dykes and larger ditches and pools. Sympetrum sanguineum (the Ruddy Darter)
is another notable species of the Essex marshes. It has a mainly south-eastern
distribution in Britain, and Essex is one of its national strongholds. During the 1970s
the species was in rapid decline and its status in Essex was the focus of some attention.
During the period of the survey, however. S. sanguineum has regained much ground in
Essex, and is now a relatively common and widely distributed breeding species. Though
it breeds in a wide range of still-water habitats, the coastal and estuarine dykes continue
to support large and important populations.
The two species of Emerald Damselflies (Lestes sponsa and Lestes dryas) also breed
extensively in the marshland ditches and pools. Both favour shallow water, with dense
emergent vegetation, an association with Sea Club-rush being very striking. Lestes
sponsa occurs in a range of other still-water sites (and a few moving-water sites, too). It is
a local species in our county, and its stations on the Essex marshes remain significant in
this local context. But in the case of Lestes dryas the borrow dykes and pools of the Essex
coast and Thames estuary not only support the overwhelming majority of known Essex
sites, but also remain of outstanding national significance for this species.
One more species. Libellula quadrimaculata, is very local in Essex. A significant
proportion of sightings have been in coastal sites, and it is known to breed at such sites
in other counties. However, as a migratory species it is liable to be sighted well away
from breeding sites, and so far conclusive evidence of its breeding on the Essex marshes
is not available. Yet another species. Brachytron pratense (the Hairy Dragonfly), an
increasingly localised species of broadland and coastal levels, has what appears to be its
only Essex breeding site in a length of borrow dyke in estuarine grazing marsh. Mention
should also he made of Coenagrion scitulum, the Dainty Damselfly. which, though now
believed to be extinct in Britain, had its only known site in a pool in estuarine marsh
near Hadleigh.
The borrow dykes, pools and ditches of the grazing marshes of Essex, then, support
fewer species than some of the best examples of other types of habitat. However,
amongst those species which do breed in this habitat are several whose marshland sites
are of great significance either in a regional or even national context. For this reason, the
best of these coastal and estuarine sites have more conservation value for their
dragonfly fauna than do many other Essex sites with a larger total of breeding species.
Fortunately, several of the most important grazing marshes are protected by The Nature
Conservancy Council or other organisations, such as the Ministry of Defence, which
are committed to conservation in their management regimes. Nevertheless, such
preserved areas are becoming increasingly isolated, as grazing marshes are converted to
arable fields, used for industrial development, port facilities, or dumping of dredged
mud. A recent survey (Thames Estuary Wildlife Conservation Group, no date) showed
that no less than 32% of the North Kent Marshes between Gravesend and Whitstable
were lost through conversion to arable by under-drainage and ploughing between 1969
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