The two genera of Harpellales (Trichomycetes) found most frequently in
Chironomidae (midge) larvae, namely Smittium in the hindgut and Stach
ylina in the midgut, are easily distinguished in most instances. Howev
er cases are reported in which Smittium trichospores extrude premature
ly as they pass through the midgut, with the sporangiospore attaching
to the peritrophic membrane and thereby leading to very limited thalli
c growth that resembles an immature Stachylina thallus. This developme
nt appears to be common in Smittium longisporum and Sm. perforatum, an
d may occur less frequently in some other species of Smittium. Methods
to identify such ''false'' Stachylina thalli are discussed.