The large pill woodlouse Armadillidium depressum Brandt, 1833 found in Worcestershire
On 8th July 2014 I noticed a Pill Woodlouse on the wall of the Volunteer Centre in the middle of Evesham. This particular individual was slate-grey and very large and on closer examination its body plates (pleonites) splayed out at the edges. When I tried to capture it, rather than rolling into a ball typical of the pill woodlice, it clamped down with its splayed plates covering its legs. This curious behaviour and large size was reminiscent of a species that I am familiar with from the quarries on Portland, Dorset, Armadillidium depressum, so I decided to take the woodlouse to check it later. I referenced A Key to the Woodlice of Britain & Ireland (Hopkin, 1991) which gives the description for A. depressum “….and often rest in a clamped position in which they remain even when disturbed.......pleonites appear splayed out like a skirt....”. Details shown of the uropods and telson from the rear confirmed that I had found Armadillidium depressum. The images 01, 02, 03, & 03 compare the common Pill Woodlouse Armadillidium vulgare with Armadillidium depressum.
This is a strongly synanthropic species and appears to be going through a range expansion. The Atlas of Woodlice and Waterlice in Britain & Ireland (Gregory, 2009) gives the distribution as having a “distinct south-west bias” and a large population is known to exist around Bristol (B. Westwood pers. comm.). So this is certainly a species to look for around the county's towns and old churches.
Interestingly Worcestershire Biogical Records Centre holds two other records:
Bredon Hill, SO9438, 1985-1986, Paul Whitehead.
Newland SO791482, 29.06.14, John Dodgson.
Hopkin, S.P. 1991. A Key to the Woodlice of Britain and Ireland. Field Studies vol 7 No. 4 Field Studies Council, Shropshire.
Gregory, S. 2009. Woodlice and Waterlice (Isopoda: Oniscidea and Asellota) in Britain and Ireland. NERC Centre for Ecology and Hydrology, Oxfordshire.
01. Armadillidium vulgare. Gary Farmer
02. Armadillidium depressum. Gary Farmer
03. Armadillidium vulgare uropods and telson. Gary Farmer
04. Armadillidium depressum uropods and telson. Gary Farmer