H. compressus Walckenaer, 1802: Males are very difficult, often impossible, to distinguish from H. simplex. Females generally cannot be reliably distinguished from similar species using morphological techniques and are usually grouped into the Halictus simplex-complex.

References: Amiet F, Herrmann M, Müller A, Neumeyer R (2001) Fauna Helvetica 9. Apidae 3: Lasioglossum, Halictus. Centre Suisse de Cartographie de la Faune, Neuchatel, Switzerland. 208 pp. Pauly, A. (2017). Clé provisoire pour l'identification des Halictus Latreille, 1804 et Lasioglossum Curtis, 1833 de Belgique (Hymenoptera Apoidea Halictidae).