supports very few species (along its Essex reaches, at least) and these are often present at
rather low densities. Significantly, however, the short stretch of the river which runs
alongside the Glemsford Pits S.S.S.I. has a well-developed marginal and aquatic flora,
and supports at least five species of damselfly. including the very local Erythromma
najas and another species. Coenagrion puella, which has not recently been recorded from
any other site along the river. The persistence of this one 'oasis' on the Stour suggests
that the decline in its dragonfly fauna may have had more to do with unsympathetic
management of river-margins and changing agricultural land-use than with water-
quality as such.
The Roding is another river long known to be of outstanding value for its dragonfly
fauna and has been carefully studied during the present survey period by D. Martin and
P. Raven. Calopteryx virgo formerly bred on the Roding but was already in decline by the
late 1940s. Apart from the loss of that species, the Roding seems to have maintained its
very impressive assemblage of moving-water species. It remains, for example, one of the
very few strongholds for Platycnemis pennipes despite being rated as class 2 for water
quality (Corke, 1984. p.117ff). and despite running for most of its length through a
mainly arable landscape. The Roding is also the subject of more immediate and specific
concern as a result of a massive pollution incident which took place in April 1985. As a
result of an accident on the M.11 Motorway, approximately 100 gallons of the extremely
poisonous insecticide 'Dursban' was spilled into the Brookhouse Brook, a tributary of
the Roding. The chemical killed thousands of fish and millions of invertebrates
throughout the length of the river downstream of the incident, and a project to monitor
the longer term effects of the pollution has been set up by the London Wildlife Trust, the
Polytechnic of Central London and the Environmental Monitoring Unit at North East
London Polytechnic. It is much too early to predict the results of this study, but D.
Martin, who has observed the dragonflies of the Roding River for several years reports a
general reduction in both species and numbers of individuals downstream from
Abridge during 1986 Only one species. Calopteryx splendens was present in significant
numbers, and showing signs of breeding activity. Upstream of the pollution incident
dragonfly populations were reported to be at about their usual levels.
B. Some Important Essex Dragonfly Sites
Before the current phase of recording-activity began around 1980. certain sites were
already recognised as of importance for their dragonflies: the Epping Forest ponds, the
Rivers Lee. Roding and Chelmer, the Thames Marshes around Leigh and Benfleet.
Hatfield Forest and elsewhere. Since 1980. with more even county-wide coverage of
dragonfly recording, it has been possible to assess the local significance of these sites.
Other sites, previously less well-known for their dragonflies, have also been discovered,
or have had their value as dragonfly sites recognised. The following sites have been
singled out for special mention, because of their range of species, because they support
one or more very local species, or because they are illustrative of the possibilities for a
particular kind of habitat. Though it is tempting to make inferences about the relative
importance of sites on the basis of this survey, some caution is necessary. Some sites.
such as several of the Epping Forest ponds, have been subject to intensive observation
over a long period by a number of observers. Others, such as some of the north-west
Essex sites, have been visited once or twice only during the survey period. Where a site
has been visited infrequently, poor weather conditions, or annual fluctuations in
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