Differences in ectoparasite composition of invasive squirrels across urban and rural landscapes, with insights into local ectoparasite acquisition

Background Urban areas are major interfaces for biological invasions, in which introduced species frequently interact with humans and synanthropic wildlife and may facilitate pathogen transmission. With continued urbanization, assessing these zoonotic risks associated with invasive species is becoming increasingly important. The Pallas’s squirrel Callosciurus erythraeus , an introduced species established in several Japanese cities, provides an opportunity to examine post-invasive patterns of parasite acquisition. In Hamamatsu City, where its invasion history and range expansion are well documented, ectoparasite assemblages were compared across urban and rural landscapes to explore how host–parasite interactions are structured. Methods Between June 2019 and January 2021, 194 squirrels (96 males, 98 females) were collected across 22 sites. All ectoparasites were recovered and identified using morphological and molecular approaches. Variations in ectoparasite assemblages were compared across urban and rural landscapes. Results Identified taxa comprised three tick species represented by Haemaphysalis flava , H. hystricis , and Ixodes columnae , trombiculid mites including Leptotrombidium spp., and one flea, Ceratophyllus ( Monopsyllus ) anisus . Non-native ectoparasites were not detected, providing no evidence of co-introduction with the invasive host. Instead, the findings were consistent with a scenario of parasite release followed by secondary acquisition of local ectoparasite species. Ectoparasite assemblages exhibited a patchy distribution, with higher diversity observed outside the urban core. Conclusions Evaluating the zoonotic risks associated with invasive hosts requires an understanding of the composition and distribution of resident wildlife that may serve as sources of ectoparasites, including potential vectors. These results underscore the value of proactively characterizing resident host communities, along with natural history and biodiversity data, to identify potential infection processes within urban ecosystems. Integrating this ecological and epidemiological knowledge into invasive species management and disease surveillance frameworks is essential for predicting and mitigating emerging zoonotic threats in urbanized landscapes.