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The Essex Naturalist
Much of Essex is intensively farmed and consists largely of arable land but
South Essex and the Colchester area are two areas of Essex known to contain a
remarkable biodiversity of solitary bees and wasps and other invertebrates. There
is little doubt that the East Thames Corridor is the most important area of
invertebrate biodiversity in the county (Harvey 1995a, 1996, 1998).
A total of 318 species of aculeate Hymenoptera (bees, wasps and ants) ate
now recorded from the East Thames Corridor in South Essex. This is 95% of the
county fauna and 5,3% of the national fauna. In Thurrock alone more than 295
species of bees, wasps and ants have been recorded in the Essex part of the two
grid squares TQ57 and TQ67. This is 88% of the county fauna and 49% of the
total British aculeate fauna, a very remarkable total indeed contained within a
total area of about one 10km square. This biodiversity is not so evident or
pronounced with ants. Nevertheless 24 species are recorded in the East Thames
Corridor out of the county total of 27 native species with modern records and
the area does contain some very important sites including Broom Hill and Hall
Hill at West Tilbury and the western edges of Orsett Golf Course (Mucking
Heath), without doubt the richest locations in Essex for grassland ant species.
South Essex and around Colchester are both areas of large conurbation with
an associated history of mineral extraction and abandonment of large scale
farming. This has resulted both in the survival of a complex of unimproved
habitats and relatively undisturbed disused mineral extraction and post-
industrial sites, which represent some of the best flower-rich and diverse habitats
remaining in the county today. The rich biodiversity of these two areas also
seems to be due to a unique combination of climatic, physical and ecological
factors. South and east Essex has the lowest rainfall and is one of the warmest
parts of the country. Average whitei temperatures are several degrees colder
than those of south western England, resulting in a greater range of temperature
and more continental climate than the rest of Britain (Jermyn, 1974). The
influence of the Thames and the Colne and Blackwater Estuaries is also likely to
be important.
The Essex side of the Thames has a series of south-facing escarpments
between Purfleet in the west and Southend to the east, with various exposures of
chalk, Thanet Sand, Thames Terrace Gravel and London Clay. The Purfleet-
Grays area has a long history of chalk extraction, with old leases dating back to
the sixteenth century and modern times have seen much more extensive
extraction of chalk and sand resulting in many abandoned exposures of different
ages. These areas have provided many invertebrates such as Hymenoptera (ants,
bees and wasps) with a complex of nesting sites and flower-rich foraging sites;
the survival of pockets of old and unimproved habitats within this "post-
industrial" landscape has provided the nucleus from which species have been
able to spread, to take advantage of the new habitats. However many ant species
seem less able to move into these new habitats and the older habitats such as
those found in the ancient Thames Terrace gravel sites at Broom Hill, Hall Hill