Oniscus asellus. Rock Creek Park, Washington, DC, USA.
Flatter than its relative the Pillbug, it is unable to roll up. Slightly different markings on exoskeleton as well.
On rotting wood
Oniscidae is a family of woodlice, including the common woodlouse Oniscus asellus. Six genera are certainly placed in the family (Oniscus, Oroniscus, Phalloniscus, Rabdoniscus, Rodoniscus and Sardoniscus), with eight others included by some sources (Cerberoides, Diacara, Exalloniscus, Hanoniscus, Hiatoniscus, Hora, Krantzia and Tasmanoniscus).