Oligolophus hanseni is normally quite a dark harvestman with a waisted saddle which becomes parallel sided after the constriction. Often the outline of the saddle is marked with conspicuous pale patches. The small trident can be nonetheless conspicuous under a hand-lens because the pale members can be accompanied by many additional tubercles. The ocularium is dark but can have some quite striking light patches on it - especially around the conspicuous tubercles, although these seldom coalesce to form clear 'eye rings'. Some individuals can be much lighter in the centre of the saddle. Legs can be conspicuously annulated - pale and dark brown.
In the field, some specimens of Oligolophus hanseni can resemble very dark specimens of Paroligolophus agrestis (with which it is often found) and this, together with the annulated legs, is a good way of picking them out for closer inspection. On close inspection the obvious tubercles of the ocularium immediately separate it from P. agrestis which only has some very small bristles (which can be almost invisible from the top). Dark specimens can have a dark bluish hue.
Although few sources mention it, separating Oligolophus tridens and Oligolophus hanseni can also be a challenge for beginners. The trident and associated tubercles are normally quite different. Although the trident members of both species are quite small, in Oligolophus hanseni they are normally conspicuously pale (even white) and, on very close inspection, tipped with black spines. In Oligolophus tridens the trident tubercles can be pale, or the same colour as the body. Oligolophus tridens can have no additional tubercles to the side of the trident and as few as two behind, but in Oligolophus hanseni there are normally more than this to the side and behind. In Oligolophus tridens the two rows of tubercles on the ocularium are often neatly delineated in white, giving the impression of two white eye-rings. In Oligolophus hanseni there are white patches on the ocularium, but these don't usually give the impression of two neat eye-rings. When viewed from above, the rings of tubercles on the occularium appear to converge in the middle in Oligolophus tridens, but in Oligolophus hanseni they appear to converge more towards the front. Some specimens of Oligolophus hanseni have patches of white bordering the saddle, which don't occur in Oligolophus tridens.
Oligolophus hanseni is widespread in the UK with good numbers being found in the north - see the distribution map of the Spider and Harvestman Recording Scheme . In Europe it has an 'Atlantic' distribution being associated with countries in the west and is absent from the far north and south.
Oligolophus hanseni is most strongly associated with woodlands and is said to be particularly found in Scots Pine, but can also be found on heathland and in parks and gardens.
Adults occur from August to December with peak numbers in November.
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.