Porcellio spinicornis Say, 1818

Distribution

Porcellio spinicornis occurs widely throughout Britain and Ireland and is locally frequent (but remains under-recorded in many areas). 

Habitat

It favours dry, relatively exposed, calcareous substrates.  Typically, this is dry limestone or loosely mortared walls, but also quarries, cuttings, cliffs, limestone pavement, and occasionally on trees with calcareous bark (such as Apple Malus or Lime Tilia).  It is often associated with human habitation and frequently ventures indoors.

It can be found on walls by lifting capping stones or amongst rubble and beneath stones lying on hard calcareous substrates.  It can be much easier to find at night (torch-light surveys) when it is active on the surface. 

This summary is based on the detailed account in Gregory (2009).