14
A REMARKABLE JUMPING SPIDER FOUND IN ESSEX AND THE IMMINENT
LOSS OF ANOTHER IMPORTANT SITE IN THE EAST THAMES CORRIDOR
To the west of the old power station at Barking there is an area consisting of old
pulverised fly ash (PFA) lagoons over former grazing marsh which supports interesting
plant communities and an important invertebrate fauna. 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 together with some quite remarkable dune-like
formations resulting from weathered and compacted PFA. The communities that have
developed on the PFA substrate, despite similarities are very different to those to be found
at the PFA lagoons at West Thurrock, where a Saltmarsh flora grades into drier grassland
and scrub with many calcicole plants dominating.
During June this year a male of the Nationally Scarce (Notable A) jumping spider
Synageles venator was taken in the dune-like area near sedge and Phragmites. This is the
first record of this ant-mimicing spider in Essex and not one I would ever have predicted!
Most records are from the west coast where it is known from dunes and fens in S.Wales
and Devon & Somerset but there are old records for Yaxley and Woodwalton Fens. Peter
Merrett, our national spider authority tells me that the nearest other record would appear
to be in the Rye area in East Sussex.
Despite the apparently barren and unpromising nature of PFA it does revegetate naturally
and will eventually develop into woodland after abandonment. In common with other
more natural habitats it is the successional stages which provide much of the conservation
interest and ultimately management would be needed to maintain these stages, which
often include large populations of orchids such as Southern marsh orchid. The friable
substrate is used by aculeate Hymenoptera as a sand substitute for nesting and the poor
substrate encourages the development of flower-rich plant communities important for
foraging and hunting.
Despite their ecological interest these habitats are obviously viewed as 'Brown Field'
sites and are under much greater threat of development than the rest of our decimated
nature conservation resources. Part of the Barking PFA area has been a London Wildlife
Trust reserve, but apparently the whole site will soon be cleared and developed for a
massive housing complex, planning permissions having been in place since the 1980s.
The Balking Levels to the east of the power station have already largely been developed
for housing and soon little natural or semi-natural habitat will remain. The loss of
biodiversity in this area of south-west Essex will be huge and will further fragment the
nationally important invertebrate populations present in the East Thames Corridor.
The majority of invertebrate records available have been made since 1996 and much more
material remains to be identified. The Invertebrate Index and Species Quality Index
(measures of the national rarity and diversity of the fauna) for the species of aculeate
Hymenoptera, Diptera and Arachnida recorded from the PFA lagoon area totals at least
2330 and 12.7 respectively, veiy high figures which compare favourably with some of the
best sites in the East Thames Corridor. This includes 6 RDB species, 16 Nationally
Scarce and 52 Nationally Local species. Apart from the very high biodiversity of other
rare species present there is the RDB1 Tachinid fly Gymnosoma nitens which is parasitic
on the Nationally Scarce bug Sciocoris cursitans, and a very large population of the
Silvery leaf-cutter bee Megachile leachella, nesting in the weathered desert-like areas of
PFA and foraging on Birds foot trefoil.
I hope to be able to provide a more detailed article on the invertebrate fauna of this
interesting site so that at least naturalists in the future will have access to data on what has
been lost as we approach the new millenium.
Peter Harvey
Essex Field Club Newsletter no. 26, August 1998