Porcellio spinicornis Say, 1818. An Isopod enigma in Worcestershire

Gary Farmer

Porcellio spinicornis is a relatively large species of woodlouse resembling the common Oniscus asellus but with yellow and brown mottled pattern and a conspicuously dark head. The dark head could cause this species to be mistaken for Philoscia muscorm. P. spinicornis is a species found widely across Britain usually associated with calcareous substrates and is particularly common in parts of the Cotswolds (Gregory 2009).

In Worcestershire this dependency on limestone areas limits the distribution of the species and I had only ever found it on Bredon Hill and (what I considered unusual) once on the outside wall of my house in Redditch.

In March 2015 Brett Westwood sent a photo (01) of a Porcellio spinicornis which he found in his house in Stourbridge. He commented that “For the second time in my life I’ve found Porcellio spinicornis, and once again it was on the stone fireplace in the living room. Apologies for the poor picture....this was a small specimen ... but you can clearly see the black head and the squiggly cream markings on the body. Without a lens it looks rather like an unstriped Philoscia muscorum, but doesn’t run fast. My first record three years ago was confirmed by John Meiklejohn. Must be under-recorded?”

Further reading of Steve Gregory's 2009 atlas of Woodlice and Waterlice in Britain and Ireland uncovered the following information. “Porcellio spinicornis can be found on walls or amongst rubble and beneath stones lying on hard calcareous substrates. It can be much easier to find at night when it is active on the surface” and most interestingly “it is often associated with human habitation and frequently ventures indoors. P. spinicornis remains under-recorded in many areas.”

So is this another overlooked Isopod in the county? Head-torches at the ready......

After writing this note I found Porcellio spinicornis near Hidcote Manor over the border into Gloucestershire on 4th May 2015 which provided an opportunity to obtain useful pictures (02, 03).

Reference

Gregory, S. 2009. Woodlice and Waterlice (Isopoda: Oniscidea & Asellota) in Britain and Ireland. Biological Records Centre. FSC Publications, Preston Montford, Shrewsbury.

Images

01. Porcellio spinicornis in Stourbridge. Brett Westwood.

02. Porcellio spinicornis Hidcote. Gary Farmer

03. Porcellio spinicornis Hidcote. Gary Farmer