Among 15 demodecid mite species (Acariformes: Demodecidae) recorded from carnivorans Carnivora, 3 species were described from mustelids Mustelidae. They are known only from single records, for which Demodex erminae has been described from the stoat Mustela erminea from Great Britain and New Zealand, D. melesinus from the European badger Meles meles known solely from Great Britain and D. lutrae discovered in the Eurasian otter Lutra lutra from Poland. The current record confirms the existence of D. melesinus, in badger from Poland, after close to one hundred years from its original description, as well as the first detection of the male for this species.

Psorergates rattus Fain & Goff, 1986 has been found in the brown rat Rattus norvegicus (Berkenhout, 1769) in Poland. The species has previously been found only once, in the tail base of the brown rat in the United States. In the present case, ten rats from two localities in Poland (Pomerania) were examined and infestation was discovered in 20% of them, with a total of 12 mites found. This is not only the first discovery of the species in Poland and the second globally, but also the first observation of representatives of Psorergatidae in rodents of the genus Rattus in Europe. Moreover, immature specimens of P. rattus have been observed for the first time. The infestation was asymptomatic, although in the earlier study mange was observed despite the relatively low density of the mites, which indicates a potential pathogenic threat not only to wild rat populations, but also to laboratory animals and pets.

The bat skin mites from the closely-related Demodecidae and Psorergatidae families occur synhospitally, populating the same host species and perhaps neighboring microhabitats. However, data on their occurrence and parasitism are fragmentary and dispersed. Thus far, 27 Demodecidae and 18 Psorergatidae species have been described, but the coexistence of mites from both families was only demonstrated in six species of bats. This article presents a description of Demodex pusillus sp. nov. from Nyctalus noctula, including a new host record (first observation of demodecid mites in Nyctalus) and a new record concerning the occurrence of Psorergatoides kerivoluae in Plecotus auritus. It also includes an updated global checklist of the occurrence of Demodecidae and Psorergatidae in Chiroptera, including data on their records/distribution and location in their hosts. In both studied families, the mites exhibit preferences, and even topographic specificity, colonizing different microhabitats in the host, including the eye region (e.g., Meibomian glands of the eyes, corneal surface and eyelid vault), wing membranes and hairy skin on the body. Such colonization of separate microhabitats enables different species to co-occur within the same host, while the total number of parasites determines the level of parasite load, with higher levels being associated with the incidence of disease symptoms. It is worth mentioning that Demodex pusillus sp. nov. is the smallest known representative of the Demodecidae family and one of the smallest animals (70–80 micrometers in length).

The present study describes a finding of the demodecid mite Demodex phocidi in the seal Phoca vitulina in the Baltic Sea. This is the first identification in Europe and the second in the world. This is also the first observation of the Demodecidae family in the pinnipeds outside North America. A high density of demodecid mites was observed in the skin of the examined seal, but no symptoms of parasitosis were observed. Our findings also supplement the taxonomic description and morphometry of D. phocidi.

Only six parasitic species of Demodecidae mite have thus far been described from the Soricomorpha, these being associated with the common shrew Sorex araneus Linnaeus, 1758, and the Mediterranean water shrew Neomys anomalus Cabrera, 1907 (two species from each host), and with the lesser white-toothed shrew Crocidura suaveolens (Pallas, 1811) and the European mole Talpa europaea Linnaeus, 1758 (one from each host species). Presently, Demodex crocidurae, a new species, has been described from the territory of Poland for C. suaveolens; in order to confirm its validity, it was necessary to redescribe D. talpae Hirst, 1921, from T. europaea, a demodecid species first described by Hirst in 1921 from England and then noted only in Poland. Both species colonized the hairy skin of the body in their hosts, where no disease symptoms of infestation were observed. However, D. crocidurae showed higher infection parameters (prevalence 100%, mean intensity 11.7, intensity range 3–26 individuals) than those of D. talpae (30.0%, 4.7, 2.0–8.0), possibly due to different host biology.