This species is found in tropical lowland forest and hill forest, and is presumed to be a foliage gleaning insectivore (Bonaccorso 1998). All species of Kerivoula show a strong preference for intact closed forest habitats and a low tolerance for habitat degradation and fragmentation. Until proven otherwise, it should be assumed that populations of K. agnella will persist only in relatively intact forest habitat.

This poorly-known species is endemic to Papua New Guinea and has been recorded from the islands of Fergusson (1,280 km²), Misima (259 km²), and Woodlark Islands (793 km²). There is an unconfirmed record of the species from Sudest Island because the single collected specimen has been lost. Only a few individuals have been collected in total and the species was last captured (on Fergusson Island) in 1956 (Flannery 1995a). Considerable survey effort within the known range of K. agnella by teams from the Australian Museum through the 1990s failed to detect any extant population. Although some surveys used harp traps, acoustic bat detectors were not used. No subsequent surveys have been carried out for K. agnella, despite substantial mining exploration and operations on several islands. It is recorded from sea level to 700 m asl. Given its occurrence on Fergusson Island of the D’Entrecasteaux Group it could also be present on one or both of Goodenough and Normanby Islands but this should not simply be assumed. 

The species is not known to occur or likely to occur in any protected areas. Historic sites should be protected and/or restored to provide important habitat for the species assuming it is still in the area. Additional research is needed into the species distribution, trends, threats, and ecology.