Description and notes
Lasius brunneus was first recorded in Britain by Donisthorpe in 1923 (Donisthorpe, 1927). Workers of this species look superficially like the common black garden ant L. niger but can be distinguished by, amongst other characters, their lighter brownish-red head and alitrunk contrasting with a dark gaster. L. brunneus is also almost exclusively found nesting in old trees or timber.
Lasius brunneus has only been recorded from central and southern English counties, from Essex to Shropshire. The reasons for this restricted distribution are not clear as apparently suitable nest sites can be found across Britain. There may well be other influences operating on this distribution which have yet to be identified. Lasius brunneus appears to be closely associated with a few species of ant-tended Homoptera and this may affect its distribution. The similarity in appearance between L. brunneus and other small dark Lasius, along with its timid, retiring nature and nesting biology may have led to under-recording. Overseas, from southern Scandinavia and Russia south to North Africa and Arabia, and east to the Himalayas and Japan.
Status (in Britain only)
The species is currently listed as Nationally Notable (Na) (Falk, 1991).
Most recorded flights have occurred in June or early July and are reported to take place early in the day. Winged gynes and males have been found running excitedly over the bark of infested trees but do not appear to conduct the mass swarming flights of species such as L. niger.
Workers are fugitive and rarely seen away from their host tree or even on its surface. Most activity occurs in bark crevices or tunnels under the bark where the ants tend large tree aphids such as those of the genus Stomaphis. The excreta of these Homoptera forms the majority of their diet, although they may also take other small insects found on or under the bark such as psocids and beetle larvae.
Habitat and nest sites
Nests are usually found within mature but still living trees; they have also been found in stumps, hedgerows and timber framed buildings. The ant does not appear to be restricted to any particular tree species but nests are more commonly associated with oak. Often the only outward signs of a tree being inhabited are small piles of frass resulting from excavations within the tree. Tunnels created by the ants can be found by removing the bark but the nest itself is difficult to locate and can be deep within the roots, trunk or boughs. The ants are unaggressive and rapidly disappear into their tunnels when disturbed. Where it is found, many suitable trees in an area can be infested with L. brunneus. Queens of this species are rarely found and indications are that there is only one or very few per colony.
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