The Yellow Meadow Ant Lasius flavus: spatial analysis of its nest distribution
STEPHEN MOORE
Hawkwood Lodge Field Centre, Chingford, London E4
Introduction
The Yellow Meadow Ant Lasius flavus, is known to build colonies comprising between 10,000 -
24,000 individuals. They are often associated with sites of old pasture or meadows.
Nests, although starting circular, have been shown to take on an elliptical aspect with later years of
building and, in this country, to align themselves along an cast - west orientation as the ants build
towards the dawn sunshine. It is the morning sun that is considered more important as it appears to
be a major factor in warming the nest up quickly after the relative cooling of the nest during the
night. With initial building taking place at up to 10cm a year in height, it can take up to 20 years for
nests to reach their maximum height and size, with some individual nests attaining over 0.5 metres
in height and 1.0 metres in diameter.
The ant mound creates a larger surface area during daylight hours for collecting incident solar
radiation, whilst at night there is a reverse flux. While it is true that this reverse flux will involve
losing heat, surface vegetation can help reduce this and. depending upon the vegetation height, can
have a marked effect upon heat deprivation. On calm nights after rain it has been suggested that
nest temperatures can actually be increased by 1 -2° C as a vapour mist forms in and around the
anthill and that this can reduce outward radiation as latent heat is released during condensation.
This seems to support field observations of colonies showing a preference towards sites with a high
relative humidity. This will naturally enhance the working properties of the soil as well as guarding
against desiccation of the young in the early stages of growth.
Excavation takes place at depth, with new material from the subsoil manifesting itself at the surface
as a bright and friable deposit, easily broken between the fingers. This new mixture of aerated soil
interwoven with roots from the ground and herb layers provides a good insulating material for the
colony's home and certainly helps in ameliorating adverse temperature differentials. This new
fresh tilth also provides an idle opportunity for ruderal plants (e.g. Stellaria media, Stellaria
graminae. Veronica serpyllifolia) and in particular some of the grasses (e.g. Agrostis tenuis, Festuca
ovina, Molinia caerulea) to quickly become established. Thus a protective sward is provided to the
surface of the anthill, as well as structural support for the underlying chambers and galleries. Some
workers have reported increased soil acidity that has resulted on areas supporting large populations
of Lasius sp.
Study area
An area of old meadow land was selected which lay across the north and south sides of a small
symmetrical V-shaped valley at Yardley Hill on the west side of Epping Forest (TQ383 957).
Students identified the south-facing slope (Yardley Hill, 6°) as possessing a relatively large number
of anthills (the majority of which were occupied by Las ins flavus). Other colonies of the same ant
were also identified on the north-facing slope (Daiscy Plain, 8°). Initial observations indicated that
the number and distribution of the north-facing colonies showed some marked differences when
compared to their south-facing counterparts. Each anthill was sampled on Daisey Plain and some
Essex Naturalist (New Series) 19 (2002)
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