Length: 3-9 mm
Members of the subfamily Donaciinae can be hard to identify to species or even to genus. Identity of the host plant can sometimes help make the ID. Otherwise it may be necessary to take the beetle in hand and examine it with a hand lens, working one's way through a key in the specialized literature.
Members of Donaciinae are elongate, with ten rows of punctures on each elytron. The pronotum is narrower than the elytra. Legs are notably long. Colors are usually metallic bronzy or coppery, occasionally greenish or bluish. The beetle's underside is covered with a fine, silky pubescence that helps repel water. These beetles' host plants are water plants such as reeds, cattails, and waterlilies.
Some key traits of the genus Plateumaris: the elytral apices are usually rounded rather than squared off. Further, at the apex of the elytra, the suture seems irregular because the sutural bead is expanded: the elytra "gape" a little. The host plants vary, and include a number of aquatic and marsh plants, but do not include Water Lily.
Insects of West Virginia