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.
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.
In Britain no parasitic ants are known to be associated with L. brunneus, although the species has been recorded acting as host for temporary social parasitism by L. umbratus queens.
1998