102
The Essex Naturalist
Habitat and Ecology
Seifert describes L. alienus s.s. as associated with chalk grasslands. The ant has
been found at the two sites in Essex in thermophilic conditions on dry grasslands.
The Bartlow Hills are four round tumult that survive from a group of seven or
eight. They used to be renowned tor a rich chalk grassland flora, with Purple-
stemmed cat's-tail grass, Field fleawort and Purple milk-vetch surviving until the
1850s or 1860s and Pasque flower surviving until the 1920s (Corke 1984).
Today they are surrounded by secondary woodland but three of the tumuli are
still covered by chalk grassland providing conditions suitable for this ant.
The Hadleigh Downs population is more interesting because neither Benfleet
and Hadleigh Downs consist of chalk grassland but instead are largely dry south-
facing scarp grasslands on clays and gravels facing the Thames Estuary. The
ridge on which the castle was built consists of London clay underlain by gravels
and is extremely unstable with a history of landslips which eventually caused the
ruin of the castle. The site of the Lasius alienus population is immediately below
the English Heritage fence where the ground probably consists of a mixture of
London clay, the infilling rubble on which the walls and kings chamber of the
castle were built and parts of the masonry itself (R.G. Payne pers. comm.).
Whilst it is possible that the calcareous nature of the masonry and mortar affects
the surrounding ground, this is also the site of the RDB3 spider Haplodrassus
umbratilis which is otherwise known only from dry heathlands in Dorset and
Hampshire (Merrett in Bratton 1991). Indeed the whole Benfleet Downs-
Hadleigh Castle area supports a curious mixture of invertebrates more usually
associated with calcareous grassland such as the Notable spiders Meioneta
simplicitarsis, Phrurolithus minimus and Trachyzelotes pedestris (Merrett 1990)
together with species associated with heathlands. The remaining scarp below
the castle is semi-improved cattle-grazed pasture without the same nature
conservation value.
Threats
Old unimproved flower-rich chalk grassland turf is virtually absent from modern
Essex and the ant has not been found in old chalk quarries in the county. It is
likely therefore to always be a rare species in Essex and the habitats at its two
known sites are vulnerable to scrub invasion through lack of management and
degradation through public pressure and unsympathetic management.
Lasius brunneus (Latreille)
National status Scarce Na County status Essex Scarce
Threat status Regionally Important Frequency Ratio 1.3
Tetrad Percentage 1.9% Recorded 1km sq. percentage 4.5%
Distribution
The ant is listed for S and N Essex in Falk (1991). There are recent records from
twenty two localities especially in the Epping Forest and Brentwood areas but as