Ilybius vittiger (Gyllenhal) is given as a new combination from Agabus. The larva of this species is described from north Swedish material. Descriptions are given of all 3 larval instars based on reared specimens and characters are given for the separation from other Ilybius larvae. Information is given on the natural history and distribution of I. vittiger. Larval characters within the genera Agabus and Ilybius are discussed and a new character for the separation of the 3rd instar is proposed. Some adult characters of generic value are discussed.