Phymatodes testaceus (commonly known as the tanbark borer, or the violet tanbark beetle) is a transpalearctic polymorphic species of beetle in the subfamily Cerambycinae in the longhorn beetle family. The P. testaceus imago is typically 6–16 mm in length. Their eggs are 1 mm long, and in athwart 0.5 mm. Larvae of the species are 10–18 mm long and 2.1 mm wide. Pupa are 9 mm long, and the abdomen is 2.8 mm wide.