Proisotoma minuta is a greyish brown, common and widespread species that is usually found in decaying organic matter (Fig. 1). It can occur in large numbers in the soil of flower pots inside houses and glasshouses and reaches a maximum length of 1.1 mm. The eyes have 8+8 ocelli. The manubrium has 1+1 ventral manubrial setae and there are six ventral setae on the dens (Fig. 2). The mucro has three teeth (Fig. 3).
In July 2003, Steve Hopkin was sent a sample of live Proisotoma minuta extracted from a borehole in old sawmill waste on a landfill site. The number of springtails was quite phenomenal (Fig. 1). The layer of individuals on the surface of the groundwater from the borehole was several centimetres deep.
There is one other species of Proisotoma on the UK list, Proisotoma tenella, of which Steve Hopkin found one specimen in the NHM slide collection, mixed in with Proisotoma minuta from 'mushrooms' in Penrhyn, Bangor, North Wales. Proisotoma tenella has 8+8 ocelli, differing from Proisotoma minuta in its 3+3 ventral manubrial setae, numerous setae on the ventral side of the dens and mucro with two teeth (Fig. 4). Carpenter (1908) recorded Proisotoma tenella feeding on tobacco and bulbs in Ireland, but no specimens survive. P. tenella is probably a 'tramp' species accidentally introduced around the globe.