Ants round my home, woodlice in theirs...

My entomological side is getting twitchy - after months of near-invertebrateless cold, I can see a variety of multi-appendaged beasts crawling, flying and generally being busy. So, during a trip to dig the allotment, I couldn't help noticing quite a bit of ant activity. They haven't found the house (i.e. the kitchen) yet but are busily working in the garden, around all kinds of cracks and various bits and pieces. As I left through the back gate, there were even some that had helpfully started work at head height (in and around two bolt-holes in a gatepost) allowing me to look at them closely without crouching down: most thoughtful...

Black ants busy around a hole in a gatepost.

Looking more closely, it seemed as if they were clearing out the remains of previous occupants - there looked to be bits of woodlouse and spider coming out. Closer still, building work was going on with 'cement' plates being formed inside the hole - luckily I managed to capture one ant placing a mouthful (mandible-ful?) of building material...

Note on the left - one ant placing building material

They look like one of the common dark garden species, but it's always worth checking so I brought a couple indoors to see if I could key them out (using Skinner & Allen 1996). The single-segment waist with well-developed petiole (a little plate sticking up from the waist), circular spiracle towards the rear of the propodeum (segment just in front of the waist) and a lack of rows of bristles on the underside of the hind tibia brought me to the genus Lasius (not unexpectedly...). From there, various features including the presence of standing hairs on the antennal scape and hind tibia (but not the double rows seen in other groups) took me to the common species L. niger.

Hind tibia with standing hairs

Head, including antennal scape with standing hairs (see below the eye)

OK, so I've been distracted - time to dig the allotment and off I go... digging (finally) takes place and I'm almost finished when I notice (a) some orange-yellow ants and with them (b) some tiny white woodlice. This looks straightforward enough - the ant is Lasius flavus nesting in the grassy path and the woodlouse is the Ant Woodlouse Platyarthrus hoffmannseggi.

L. flavus and P. hoffmannseggi - both around 3-4mm long

P. hoffmannseggi - the yellow colour is just due to lighting/image processing...

P. hoffmannseggi is an interesting beast - it is white (in the top photo you can just see dark gut contents through its dorsal surface), blind and lives closely associated with ants of almost any species (Hopkin 1991), often found in their nests where it may feed on pellets regurgitated by the hosts (Williams & Franks 1988) and/or may be a more general scavenger in the 'rubbish-dump' parts of nests (Pontin 2005). It has also been noted as following lines of ants when nests have moved (Donisthorpe 1927). This is unusual behaviour for a woodlouse (it is the only myrmecophilous - 'ant-associated' - woodlouse in Britain), but not unique - in Malaysia there is a species of Exalloniscus which 'hitchhikes' (maybe 'stows away' is more accurate) on the pupae of ponerine army ants. Although not often seen without digging, it is fairly common in southern England and Wales, becoming scarcer northwards (will climate change extend its range, and if so, how does it disperse?). Beyond this, little is known about P. hoffmannseggi - an area for a keen researcher to work in maybe?

References

Donisthorpe, H. St. J. K. (1927). The Guests of British Ants.Routledge, London. [interesting if you can find it, but can be expensive]
Hopkin, S. (1991). A key to the woodlice of Britain and Ireland. Field Studies 7(4): 599-650. [this has also be published in separate reprint form]
Pontin, J. (2005). Ants of Surrey. Surrey Wildlife Trust, Woking. [another volume in the excellent series of Surrey atlases]
Skinner, G. J. & Allen, G. W. (1996). Ants. Richmond, Slough. [excellent keys to British species]
Williams, T. & Franks, N. R. (1988). Population size and growth rate, sex ratio and behaviour in the ant isopod Platyarthrus hoffmannseggi. Journal of Zoology 215: 703-717.