Nemastoma bimaculatum is a very distinctive little harvestman in the British fauna being the only uniformly black species, usually with two conspicuous, distinctively shaped white patches on the dorsum. An all-black occassional form occurs without any white patches (form unicolor). The body is slightly flattened and granular in appearance. The ocularium is quite indistinct. Males can be separated from females by the presence of an apophysis on the distal end of the basal segment of the chelicera (but a good view is required on living specimens).
Wijnhoven (2009) describes several other very similar species that occur on the continent. It would be prudent to take occasional specimens of putative Nemastoma bimaculatum in Britain and check against these continental species since so many species of harvestmen appear to have undergone, or be undergoing, range changes (assisted or otherwise).
Nemastoma bimaculatum is ubiquitous in the UK - see the distribution map of the Spider and Harvestman Recording Scheme . In Europe it has an 'Atlantic' distribution, i.e. is found in western Europe down as far as northern Spain.
Nemastoma bimaculatum requires humid microhabitats and dwells in open soil, leaf litter moss etc. It can easily be found in woodland by sieving leaf litter or simply turning stones, wood and other things in contact with the soil, but can also be found in similar moist microhabitats away from woodland.
Not only is this species found everywhere in the UK, but adults have been found in every month of the year. There is however a clear peak in records around September and a trough around February.
Hillyard, P. D., & Sankey, J. H. P. 2005. Synopses of the British Fauna (New Series) No. 4: Harvestmen. Third Edition.Field Studies Council, Shrewsbury.
Richards, P. 2010. Guide to Harvestmen of the British Isles. Field Studies Council, Shrewsbury.
Richards, P. 2017. Tabular key for Identification of British Harvestmen (Opiliones). Unpublished.
Wijnhoven, H. 2009. De Nederlandse hooiwagens (Opiliones). Nederlandse Entomologische Vereniging.