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.