Platyarthrus hoffmannseggii is a species of woodlouse which is closely associated with ants' nests, particularly those of Lasius flavus, Lasius niger and species of Myrmica, where it feeds on ant droppings or mildew.

[1] It is white, 4 millimetres (0.16 in) long,[1] and has a distinctive oval shape and short antennae.

Its distribution appears to follow those of the ants with which it lives, and the British Isles are the north-westerly limit of its range.

Preserved specimens are also sometimes confused with dwarf isopods of the genus Trichoniscidae, due to their small size and similar appearance.

[5] This may be due to the fact that it typically lives in ant hills, in total darkness.