The fifth instar of Entomophthalmus rufiolus (LeConte, 1866) (Coleoptera: Eucnemidae: Melasinae: Dirhagini) is described and illustrated. This is the first larval description for the genus Entomophthalmus Bonvouloir, 1872. The description is based on larvae collected from pieces of rotten sugar maple (Acer saccharum Marshall; Aceraceae) collected in two Wisconsin counties, as well as rotten Quercus sp. (Fagaceae) and basswood (Tilia americana L.; Tiliaceae) logs in Dane County. Adults were reared from from larvae in wood placed in plastic bags and associated with preserved larvae found in the field. Biological information is provided and external morphology of immature E. rufiolus is compared with Rhagomicrus bonvouloiri (Horn, 1886) and other similar Nearctic eucnemid larvae.