This species is visually identical to Lasius niger without optical aid, but differs by having a sparsely-haired Clypeus compared to Lasius niger. Confirmation is easy having a specimen under the microscope, or good close up photographs. It is likely that most Lasius niger-type ants collected from shady/damp situations in woodland, will likely turn out to be this species. It does not have the same affiliation to synanthropic habitats as Lasius niger.

For over a century, the only Nottinghamshire record of Lasius platythorax was from Langford Moor near Newark in 1914. This was re-identified almost 100 years later, from a specimen retained in the Natural History Museum in Dublin Museum by Mike Lush in 2007. The county's only modern records, appear to be from Budby South Forest in June 2024 (Clark, G.) and again in April 2025 (Pendleton, T.A.). This obviously under-recorded ant has also been found at Misson Carr in April 2025 (Pendleton, T.A.) and further surveys are underway to confirm/find more sites in Nottinghamshire.