Folsomia 'bisetosa' is a scarce species with only two confirmed - and very different - UK localities (Skokholm Island and Wolverhampton). It is white and blind (0+0 ocelli) and reaches a maximum length of 1.1 mm (Skokholm specimen). The body setae are very short and the ratio of the length of the longest setae at the tip of the abdomen/length of mucro is only about 2.0. The manubrium has 2+2 apical ventral (anterior) setae arranged longitudinally (Fig. 1). The dens has 12-19 ventral (anterior) setae and 5 dorsal (posterior) setae with three at the base of the dens and two in the mid dorsal region (Fig. 2; hence bisetosa). The PAO is quite broad and is shorter than the width of ant1 (Fig. 3).
Potapov (2001) says that Folsomia bisetosa is a circumpolar species and that records from 'more southern areas' ….. 'probably refer to other, undescribed species'. Thus although the British and Irish specimens of Folsomia 'bisetosa' correspond closely with descriptions of Folsomia bisetosa in the literature, it seems likely that they represent another (possibly undescribed) species.