Platyarthrus hoffmannseggii

CRUSTACEA > MALACOSTRACA > ISOPODA > Oniscidea > Crinocheta > Platyarthridae

Platyarthrus hoffmannseggii is a small, up to 4mm long, blind and eyeless, white woodlouse with a distinctive oval, continuously outlined, somewhat flattened body that often appears yellowish or has dark marks along the back where the gut contents are showing. The dorsal surface is finely granular although, from my limited experience, in some individuals it looks smooth, which may be a trick of the light or an effect of needing to use flash when photographing them.

As the common name suggests, this species is typically found in close proximity to ants such as under stones that are alongside a run or nest or, perhaps more frequently, actually in the nest living amongst the colony. There doesn't appear to be any particular association with any specific type of ant as they have been recorded with many different species with the only notable observation being that the ants in question tend aphids both above and below ground. The woodlice don't feed on the aphids, but they do feed on waste matter within the nest thereby providing a free cleaning service for the ants. The most common associations appear to be with Lasius flavus, Lasius niger, and various Myrmica species.

Platyarthrus hoffmannseggii is primarily a central and southern species that occurs in pretty much any habitat where there are suitable ants' nests, but with records suggesting that open sunny locations such as semi-natural grasslands, waste ground, gardens and churchyards are more favourable locations that woodland, which is where I'd been looking without success. Yet on a particular woodlice-targeted visit to Portland I managed to find them in two different ant nests as can be seen below.

New species added, Sept.26 (v.1)