Philoscia muscorum is one of our commonest species of woodlouse - so common that it is one of the "Big Eight" species that zoologist Steve Hopkin decided to give an English name to - the Common Striped Woodlouse. And boy, does that go faster stripe down the back work - this is very much the Usain Bolt of woodlice. The stripe and the speed makes it easy to recognise, but if you're still not sure, look closely at the tips of the antennae, which have three segments in this species.
A closely related species of woodlouse, Philoscia affinis, occurs in Europe but not in the UK. And then ... zoologists at the Royal Belgian Institute of Natural Sciences examined a specimen of P. affinis ... which was collected in England in 1985! So they decided to take a short holiday in the UK in 2017 looking for woodlice (as you do), and visited parks and ancient forests in Cambridgeshire, Essex, Greater London, Hampshire, West Sussex and Wiltshire. Sounds nice. Oddly, they didn't visit Salisbury Cathedral with its famous 123 metre spire, so I think we can trust these guys. And of course, being highly trained woodlice operatives, they were able to find Philoscia affinis, although they're not common. Since then, keen woodlice fans have found P. affinis at quite a few locations in the UK, and it's a daily topic of conversation in the Keen Woodlice Fans Facebook Group. So here's the NatureSpot Christmas Challenge: get out there in the leaf litter and find Philoscia affinis in VC55!
Both Philoscia muscorum and Philoscia affinis are medium-sized (up to 11 mm long), have a stepped body outline and three segments at the tip of the antennae. However, Philoscia muscorum has a distinctive black head with a small yellow spot on the rear of the head while the head of Philoscia affinis is mottled brown, similar to the rest of the body. There are other subtle diferences between them so to be sure we have found this new species in Leicestershire or Rutland, if you think you've found one, send us some photos but also keep the specimen and we'll examine the 7th leg of a male under the microscope for you (who knew woodlice were so complicated?).
Are you up for the challenge? While you're at it, you can burn off some calories!
Segers, S., Boeraeve, P., & De Smedt, P. (2018). Philoscia affinis Verhoeff, 1908 new to the UK (Isopoda: Philosciidae). Bulletin of the British Myriapod & Isopod Group, 30, 21-25. https://biblio.ugent.be/publication/8544985/file/8544986.pdf