Hystrichopsylla schefferi

Distinguished from the very similar Hystrichopsylla gigas dippiei by the number of spines in the pronotal comb: H. schefferi has 46 spines, while H. g. dippiei has 36. Its exclusive association with the mountain beaver and restriction to the American Northwest further aid identification. Its exceptional size (up to 13 mm) distinguishes it from nearly all other flea species.

Adults measure up to 13 mm (0.5 inches) in body length, making this the largest extant flea species. The body is laterally compressed, typical of fleas. The pronotal comb bears 46 spines, a diagnostic feature distinguishing it from closely related species.

Restricted to the range of its host, the mountain beaver, which occupies moist coniferous forest environments in the Pacific Northwest. The host requires dense vegetation near water sources and constructs burrow systems in deep, friable soil. The flea likely occurs within host burrows and immediate surrounding areas.

Native to the American Northwest, with range coterminous with that of the mountain beaver (Aplodontia rufa). This encompasses coastal and montane regions from southwestern British Columbia through western Washington and Oregon to northwestern California.

Blood-feeding parasite; feeds exclusively on the mountain beaver (Aplodontia rufa).

• Aplodontia rufa - obligate parasiteMonoxenous association; the only known host. Range of flea is coterminous with host distribution.

Ectoparasite of the mountain beaver. As a member of one of the oldest flea lineages, it represents a retained ancestral host association pattern compared to more derived flea families with broader host ranges.

No known direct significance to humans. Not reported to bite humans or transmit pathogens to human populations. Its conservation status is indirectly tied to that of its host, which faces habitat pressures from urbanization and forestry practices.

• Hystrichopsylla gigas dippieiVery similar and closely related species distinguished by pronotal comb spine count (36 spines vs. 46 in H. schefferi). Likely shares general morphology and possibly geographic overlap or proximity.
• Other Hystrichopsylla speciesMost congeners are not strongly host-specific and parasitize various insectivores and rodents, unlike the strict monoxeny of H. schefferi on the mountain beaver.

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life