1. Flies (Diptera) damage ungulates far beyond the injury of their bite wounds: they are vectors of diseases and cause ungulates to lose foraging opportunities due to avoidance behaviour. We can use the behavioural and physiological responses of bison Bison spp. (Artiodactyla: Bovidae), caribou/reindeer Rangifer tarandus (Artiodactyla: Cervidae), and moose/elk Alces alces (Artiodactyla: Cervidae) to assess the impacts of flies on these ungulates. Ungulates rely on morphological and physiological resistance to flies at lowintensities of exposure. However, as fly exposure increases, ungulates begin to react with behavioural avoidance in addition to increasing their physiological response. Rangifer tarandus are highly sensitive to flies and respond quickly to their presence by avoidance behaviours that incur fitness costs through reduced body mass. Alces alces are less reactive to fly exposure, enduring the presence of flies and maintaining a low loss of fitness, sometimes dying from the cumulative effects of exposure. Bison spp. may use a facultative strategy that depends upon the prevalence of flies and associated diseases in their environment. Among these strategies, variables such as the type of fly bite, presence and degree of infection, and heritability of resistance affect individual host survival. 3. Relationships between flies and ungulates can integrate multiple scales of organisation in the ecosystem to reflect system stability. Climate change is predicted to alter the species composition and seasonal phenology of flies and the associated effects of wounding and vector-borne disease on ungulate populations that are central to the functions of Arctic and temperate ecosystems in the Northern Hemisphere.

Long-standing reports of open sores on the hind legs of moose (Alces alces) have been recorded in Alaska (as well as Canada, Europe, and Michigan), eliciting concerns about causes and infection. We used histological and genomic methods to investigate the sores from 20 adult moose on the Kenai Peninsula, Alaska. We paired this with thermal imagery and molt scoring of adult moose to further describe sore formation and understand its timing. Severe, ulcerative and eosinophilic dermatitis was found in all moose with sores present, and microfilariae within intraepidermal pustules were additionally found in four samples. Genetic analysis of sores from moose revealed a previously unknown genetic lineage of Onchocerca. Adult moose molt and lose their barrier of protection against flies in June and July during peak fly activity, leaving them vulnerable and allowing the development of sores. In summary, our results indicate that the cause for the sores on the hindleg of moose is a previously unknown genetic lineage of Onchocerca, probably transmitted by black flies, in timing with the molt cycle of adult moose. These sores leave moose exposed to pathogens, making them vulnerable, and challenging their health and fitness.