A description and illustrations of the mature larva of Rhagomicrus bonvouloiri (Horn, 1886) (Coleoptera: Eucnemidae: Melasinae: Dirrhagini) are given. The description is based on mature larvae collected from pieces of rotten sugar maple wood (Acer saccharum Marshall). Adults were reared from those pieces placed in plastic bags and associated with larvae found in the field and preserved. Biological information is provided, based on literature records and personal observations. Historical accounts of larval discriptions in the Nearctic region are briefly discussed. This is the first larval description for Rhagomicrus Fleutiaux, 1902.