3
We have looked at a wide range of sites in south and north Essex and there are recent
records in the county for 334 species of aculeate Hymenoptera. 289 of these species are
recorded in the two grid squares TQ57 and TQ67 (part squares with a total area of less
than a single 10Km square!) containing sites such as Mill Wood Pit (see Newsletter No.11
), Ferry Fields (Newsletter No. 12 ) and the Thames Terraces at West Tilbury (to be
described in the forthcoming Naturalist). This is 48% of the total british aculeate fauna
and 86% of the county fauna, a very remarkable total indeed. A total of 314 species are
recorded from the East Thames Corridor squares TQ57, 67, 48, 58, 68, 78, 88 and 98,
forming 52% of the national fauna and 94% of the county fauna!
Coincidence map showing the concentration of
hymenoptera recorded in each 10Km square in Essex
(using DMAP, a computer mapping program produce
by Dr Alan Morton)
There is little doubt that this is a genuine concentration of biodiversity. Fieldwork
elsewhere in the county has identified other important sites particularly in the most
interesting area south of Sudbury, but nothing to come close to the south Essex area.
This concentration of species seems to be due to a combination of factors: the East
Thames Corridor has unique combination of climatic factors, with the lowest rainfall and
one of the warmest parts of the country, but with a greater range of temperature and a
more continental climate than the rest of Britain. 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 sands, Thames terrace gravels and London clay.
The Purfleet-Grays area also has a long history of chalk extraction, with old leases dating
back to the sixteenth century. 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 Hymenoptera 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 I believe provided the nucleus from which species have been
able to spread, to take advantage of the new habitat.
This may have been one of the main reasons traditional agriculture in the past provided
such a good landscape for many invertebrates and other wildlife. The complex of
unimproved grasslands, pasture, heathlands, woodlands and small disturbed areas created
by traditional practices would have provided a similar (but probably much richer!)
combination.
The problem now is that most of the East Thames area has already been developed for
industrial use and housing and much of what remains is threatened in the near future.
Once the area is covered with concrete there can be little optimism for the future. The
East Thames area must still have more surprises to provide, but it can only be hoped that
enough sites can be saved from development to prevent the continued fragmentation of
the habitat and allow the survival of viable populations.
Peter Harvey
Essex Field Club Newsletter No. 19, November 1996