Folsomia agrelli is a scarce species that has only been found in caves in Britain. It is white with 1+1 ocelli and reaches a maximum length of 1.3 mm. The ratio of the length of the longest setae at the tip of the abdomen/length of mucro is between 2.8 and 3.5. The manubrium has 2+2 apical ventral (anterior) setae arranged longitudinally (Fig. 1) . The dens has 8-9 ventral (anterior) setae and 3 dorsal (posterior) setae. The PAO is narrow and constricted and is slightly longer than the width of ant1 (Fig. 2).
Potapov (2001) says that Folsomia agrelli is species of high mountains in Norway and Sweden. Thus although the specimens of Folsomia 'agrelli' in the NHML collection correspond closely with descriptions of Folsomia agrelli in the literature, it seems possible that they represent another (possibly undescribed?) species.
The confirmed record from northern Scotland is from Inchnadamph Cave. The specimen was mis-identified as Folsomia 'similis'. The other confirmed record is a mature female from Ogof Cynnes in South Wales.