Length: 10-13 mm
Acilius mediatus has distinctive elytra markings. These beetles are common in bodies of water ranging from ponds and lakes to puddles in tire ruts. They are often active early in the year; the pair shown above was photographed in a puddle in mid-April.
In addition to the yellowish bar on each elytron, there is also a black bar on the pronotum and one behind the eyes. There is also a dark M between the eyes.
American Insects site