redirect public pressure away from some stretches of the water-margins, possibly by
temporary fencing or other obstacles. Over-stocking of ornamental lakes with fish or
waterfowl are further threats to a diverse dragonfly fauna, but angling as such does not
necessarily reduce the value of a site for breeding dragonflies.
(d) Flooded Mineral-Excavation Sites
The sands and gravels which overlie the chalk, particularly along the main river
valleys and estuaries of west, south-west, central and north-east Essex have long been
exploited to supply the building industry and for use in road construction. Proximity to
London, and the associated market demand for construction materials has clearly been
an important factor, as well as the geology of the county, in stimulating mineral
extraction in Essex. Sand-and-gravel workings are particularly abundant, and some
areas also have clay, brick-earth and chalk-pits. The rise and fall in demand for
construction materials also creates a rhythm of activity in the extraction industry, with a
consequence that some sites, while not worked-out, are left relatively undisturbed by the
extraction companies for quite long periods of time.
During the period of extraction, the washing process requires an ample reservoir of
fresh water, and these reservoirs, together with natural flooding of the pits left by the
extraction itself, remain to be colonised by dragonflies and other organisms when sites
are worked-out or periodically unused. Even a working extraction-site will usually
support a fairly diverse dragonfly population. Some abandoned sand-and-gravel
workings have been acquired by The Essex Naturalists' Trust as nature reserves, whilst
others are used for angling and other recreational purposes.
Flooded pits have several great advantages as potential dragonfly sites. If extraction
has taken place over a prolonged period of time, a pattern of larger and smaller pools, of
different outlines, depths and ages may be left. This makes possible colonisation by a
wide range of aquatic and marginal vegetation, such as Canadian Waterweed. Water
Starwort, Duckweeds, Pondweeds. Water-lilies. Reed-mace. Bur-reed. Common Spike-
rush and various other rushes. Surrounding the pits are generally areas of grassland and
scrub which are untouched by the pressures of commercial agriculture and are usually
rich in insect life. They are ideal hunting grounds for adult dragonflies, and provide
shelter in windy or wet weather, especially for dragonflies in their teneral phase. Of the
twenty-two breeding species of Odonata in Essex, seventeen breed, or have recently
bred in such flooded pits. A further one. Lestes dryas (the Scarce Emerald Damselfly).
has just been discovered at a gravel-pit site (breeding has yet to be confirmed at this
locality, however). Such species as Enallagma cyathigerum, Libellula depressa and
Orthetrum cancellatum are among the first species to colonise newly flooded pits, and
they are soon followed by Sympetrum striolatum. Aeshna grandis and Anax imperator (the
Emperor Dragonfly). The more richly vegetated pits may harbour Coenagrion puella
(the Azure Damselfly) and Sympetrum sanguineum (the Ruddy Darter), whilst small pits
almost choked with Reed-mace, or other emergent vegetation, and in the last stages of
drying out commonly support colonies of Lestes sponsa (the Emerald Damselfly).
A well-established and favourably located flooded gravel pit will commonly support
some seven to ten species of Odonata at any one time, and the best sites, such as the
Fingringhoe Wick Reserve of The Essex Naturalists' Trust may have as many as fifteen.
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