Passalidae is a family of beetles known variously as "bessbugs", "bess beetles", "betsy beetles" or "horned passalus beetles". Nearly all of the 500-odd species are tropical; species found in North America are notable for their size, ranging from 20–43 mm, for having a single "horn" on the head, and for a form of social behavior unusual among beetles. While the taxonomy of Nearctic species is well-known (four species in the US, and 90 in Mexico), bess beetles in other parts of the world need further study.