Seven species from the spider family Nesticidae are currently known for the Italian fauna. Three Italian nesticids belong to the newly-established genus Domitius Ribera, 2018. All these species show a restricted distribution along the Apennine mountain chain and deep adaptation to cave life. Herein, a fourth species, D. culsu sp. nov. from a single cave in Northern Apennines is described. Detailed illustrations and diagnosis of the new species are provided. Molecular and morphological analysis of both sexes of D. culsu sp. nov. supports the validity of the new species and its close relationship with the other Domitius species from the same geographical area. A close affinity with the species distributed in the Iberian Peninsula is also observed. The potential susceptibility of D. culsu sp. nov. to external disturbance, and its extremely limited distribution, makes this spider of interest for conservation.