Invertebrate survey at Gunpowder Park, the former Royal Ordnance Site in the Lee Valley
Survey and methodology
Although designed to be taxonomically wide-ranging, the emphasis during the field survey was on
target groups of habitat indicator species, most notable the spiders (Arachnida), bees and wasps
(aculeate Hymenoptera), beetles (Coleoptera), flies (Diptera), planthoppers (Auchenorrhyncha)
and plant bugs (Heteroptera). These groups of insects contain a number of rare species which have
important populations in the region and which are effective indicators of grassland, wetland and
woodland habitats.
In 2002 an initial visit was made on 8* August with Tim Hill to look round the site. The site was
then visited again on 21st August, 5* September and 5th November 2002 when assessment of
invertebrate habitat and survey work was undertaken. In 2003 an initial visit was made on 26th
March to decide on the scope of the survey work. Traps were set at sample locations on 2nd June
2003 and these were collected and reset at approximately two-week intervals until 5lh September.
On each occasion active fieldwork was also undertaken.
Active survey work entailed the standard field techniques of direct observation, sweep netting, beating,
hand netting, turning over stones and pieces of debris and 'grubbing around' at the base of vegetation
and grass roots. In order to maximise the quantity of data available, passive sampling - in the form of
pan traps and pitfall traps set in representative areas of habitat - was undertaken as well as active
fieldwork. It should be emphasized that although trapping may result in the collection of quite large
numbers of specimens, this represents a very small proportion of the numbers of invertebrates that
would be killed through natural causes, and provides important information that can then be used to
help conserve the rare species and different assemblages present. Traps are an effective means of
collecting various foraging and hunting insects and spiders and take advantage of spells of good
weather when the field worker is not present, as well as sampling ground dwelling invertebrates
active at night. The pan traps used were yellow, plastic trays placed on the ground and containing a
preservative (dilute antifreeze or ethylene glycol), and a small amount of detergent to reduce surface
tension. Insects confuse the traps with large flowers and are caught. This method is especially effective
for flies and solitary bees and wasps. Pitfall traps consisted of plastic containers containing dilute
antifreeze and a small amount of detergent were set into the ground flush with the surface.
Invertebrate habitats
Old grasslands
By far the most interesting and important grasslands are currently the old flower rich area (Area C, Plate
13) that appears to have survived the site's clean up and restoration operations and the edges of the ditch
and hedgerow at Area B, together with the band of Deschampsia and Carrot Daucus carota adjacent to
the northeast end of the Osier Marsh, and the Carrot rich edges to the path to the new hide.
Arca C contains lots of Yarrow Achillea milleifolium. Carrot, Hardhead Centaurea nigra, Teasel Dipsacus
fullonum, Hop Trefoil Trifolium campestre, docks and thistles, as well as some St John's-wort Hypericum
and Ragwort Senecio. The grassland at the edge of the ditch and hedgerow at Area B is also diverse and
provides many valuable forage resources. The Deschampsia tussocks provide valuable over wintering
sites for many invertebrates and Carrot is an important forage plant and a species that has a close
association with a number of scarce insects.
Essex Naturalist (New Series) 21 (2004)
91