Iglica gracilis is endemic to Slovenia where it is found in the caves and springs in basin of river Krka. Di Mattia (2007) reported finding this species at the karstic springs Poltarica near Krška Vas, Grospulje but shows a wider range in his distribution map of the slovenian species of Iglica covering much of the catchment of the river Krka to the junction with the Sava river.