Brown roofs for invertebrates
HYMENOPTERA Hylaeus signatus (a yellow-faced bee); this Nationally Scarce bee is mainly
recorded from southern England, with about 30 known post-1970 sites known to Falk (1991), over
half in Kent. In Essex the bee is mainly found near the Thames in post-industrial habitats and
disused mineral extraction sites where Weld Reseda luteola or Mignonette Reseda lutea occur.
There is a close association with Reseda, from which the bee collects pollen to provision its cells.
Nests have been recorded from dead woody stems of bramble and rose, in hard clay banks and
occasionally in the mortar of masonry. Apparently in Warwickshire the species does not occur in
isolated parts of the county even where good stands of Reseda occur - indicating the importance of
a continuity of habitat mosaic and the nature conservation losses that occur when fragmentation
becomes excessive, currently a massive threat in the East Thames Corridor.
HYMENOPTERA Lasioglossum pauperatum (a mining bee): Lasioglossum pauperatum is a
very local Red Data Book (RDB3) bee, recorded from several southern counties as far north as
Essex and as far west as Devon, but with very few recent records except in south Essex near the
Thames where it seems to be reasonably widespread on open unmanaged or sporadically managed
grasslands and waste ground. The bee is presumed to nest in light soils in sunny situations. Pollen
sources are unknown, but flower visits include Senecio and Crepis.
HYMENOPTERA Myrmica bessarabica = specioides (an ant): listed only for East Kent in Falk
(1991) the Red Data Book (RDB3) Myrmica bessarabica was first recorded in Britain from
Sandwich, but is now known to be more widespread in warm coastal situations in Kent and Essex.
It may be increasing in range, but identification of this and related Myrmica species is difficult and
the ant had probably formerly been overlooked in its coastal Essex locations. It favours warm,
sparsely vegetated ground in sunny situations, such as dunes, south-facing landslip grassland, south-
facing terrace gravel grassland, but more rarely has occurred on old sparsely vegetated post-industrial
habitat. The ant might eventually colonise suitable habitat on brown roofs.
Other species
Other species that might benefit from suitably designed brown roofs include Ponera coarctata the
Indolent Ant, a nationally scarce species referred to in the Lee Valley Biodiversity Action Plan. A
number of bees and wasps usually associated with dune habitats arc found in open sandy waste ground
habitats in the East Thames region, such as the nationally scarce bees Megachile leachella and the
sphecid wasps Astata, pinguis, Gorytes tumidis and its nationally scarce cleptoparasite Nysson dimidiatus.
Brown roofs that provided areas of loose sandy substrate might accommodate these species.
Spider hunting wasps, or pompilids, include various species that might benefit from green roofs,
especially where these include sandy substrate and open sporadically managed vegetation. Many
scarce beetles associated with open dry grasslands and waste ground are widespread in the East
Thames region, including a number of Red Data Book tumbl ing flower beetles Mordellistena species
that develop inside the herbaceous stems of plants such as Wormwood Artemesia absinthium.
Conclusions
Further study is needed on the invertebrate fauna that colonises brown roofs to assess the long-term
benefits that they may provide to the conservation of the nationally important invertebrate populations
that currently exist in south Essex and the East Thames Corridor, as well as the Colchester area. The
design of brown roofs, especially where they are to be used as mitigation for lost invertebrate habitat,
should incorporate the key features known to be of important to the fauna described in this paper.
Essex Naturalist (New Series) 21 (2004) 87