south western England, resulting in a greater range of temperature and more continental
climate than the rest of Britain (Jermyn 1974). The climatic influence of the Thames
Estuary is also clearly 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 sands,
Thames terrace gravels 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 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 almost certainly provided
the nucleus from which species have been able to spread, to take advantage of the new
habitats. However some 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 and the western edges of Orsett Golf Course (Mucking Heath) are
therefore extremely important. The Hymenoptera fauna may well represent an important
surviving component of a biodiversity closely associated with the various Thames Terrace
sand and gravel deposits extending south from N.E. Essex to the present-day course of
the Thames.
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 Essex today. It is worth remembering the
rich fauna recorded around Colchester by the Harwoods around the end of the last
century, when various exposures of sand and gravel must already have been extant, and
when the surrounding countryside was vastly more flower-rich than today.
The best habitats for aculeate Hymenoptera include various 'brown field' sites such as old
sand pits, brick pits, silt lagoons and PFA lagoons, especially where these are associated
with adjacent areas of unimproved or remnant old habitats. The importance of old silt and
PFA (pulverised fly ash) lagoons for invertebrates is becoming increasingly apparent. Silt
lagoons at East Tilbury and Rainham Marshes develop Saltmarsh communities that
gradually become replaced by sand-dune and flower-rich ruderal communities as the
lagoons dry out. Both have developed important invertebrate and aculeate Hymenoptera
faunas, with numerous Nationally Rare and Scarce species. At West Thurrock and
Barking there are areas of old pulverised fly ash (PFA) lagoons over former grazing
marsh with interesting plant communities and important invertebrate faunas. There are
remnant grazing marsh dykes, marshy areas of Phragmites and sedge, banks of sparsely
vegetated PFA, areas of ruderal flower-rich vegetation and scrub.
Recent work (see Newsletter No. 26: 14) has reinforced the identification of Barking PFA
lagoons as an exceptional invertebrate site including at least 6 RDB species, 17
Nationally Scarce and 52 Nationally Local species. The Invertebrate Index and Species
Quality Index for the species of aculeate Hymenoptera, Diptera and Arachnida recorded
from the PFA lagoon area totals at least 2380 and 12.9 respectively, very high figures
which compare favorably with some of the best sites in the East Thames Corridor.
Virtually none of the sites has any statutory protection and nearly all are under imminent
development threat from the 'Thames Gateway' thrust to develop the East Thames
region, especially those seen as 'brown field' sites. 'Brown field' sites are also under
threat of inappropriate management or restoration schemes which involve the creation of
amenity grassland and the planting of tree for the Thames Chase Community Forest.
Essex Field Club Newsletter No. 29, May 1999