Two new species from the genus Strongwellsea (Entomophthorales: Entomophthoraceae) that infect adult flies from the genus Helina (Muscidae) are described: Strongwellsea selandia Eilenberg & Humber infecting adult Helina evecta (Harris), and Strongwellsea gefion Eilenberg & Humber infecting adult Helina reversio (Harris). The descriptions are based on pathobiological, phenotypical and genotypical characters. The new species differ from other described members from the genus Strongwellsea by a) pathobiology as revealed by natural host species, b) morphology of primary conidia, c) color of resting spores, and d) genotypical clustering based on analysis of ITS2. The two new species have only been documented from North Zealand, Denmark.