Calliphora stelviana (Brauer and Bergenstamm) (Diptera: Calliphoridae), also known as the little bluebottle fly, has been considered a northern and montane species. Its previously known distribution was Alaska and the higher altitudes of Colorado, in the United States of America, and central Saskatchewan and northern Québec, in Canada (Whitworth Reference Whitworth2006; Tantawi et al. Reference Tantawi, Whitworth and Sinclair2017; Langer et al. Reference Langer, Kyle, Illes, Larkin and David2019). We report here the first record of C. stelviana in southern Canada, from Windsor, Ontario, Canada. Tantawi et al. (Reference Tantawi, Whitworth and Sinclair2017) collected C. stelviana in Colorado’s higher altitudes at an elevation of 3000–3300 m above sea level. In contrast, Windsor, Ontario, has an average elevation of 183 m. Little is known regarding the extent of the geographic distribution of C. stelviana, and no data are available regarding the fly’s thermal tolerances or its ecology beyond generalisations with other Calliphora species.

Calliphora stelviana can be distinguished from other species within the genus by its white calypters, a characteristic shared with only one other Calliphora species in North America, Calliphora genarum (Zetterstedt) (Tantawi et al. Reference Tantawi, Whitworth and Sinclair2017). According to Whitworth (Reference Whitworth2006), Bellardia vulgaris (Robineau-Desvoidy), a species collected from New Jersey, United States of America, will key to C. stelviana if the genera characteristics are missed.

During the fall (14 October–6 November) of 2020, we sampled 44 sites throughout Windsor–Essex County, Ontario. The sites consisted of various land-use and landscape types, including residential, commercial, waste, and wooded, with different traffic-volume levels and reported roadkill densities. At each site, a RESCUE POP! Fly Trap (Sterling International, Spokane, Washington, United States of America), which Brundage et al. (Reference Brundage, Bros and Honda2011) and Ly (Reference Ly2019) report to be the most effective live collection trap design among commercially available fly traps, was baited with 15 g of porcine liver that was aged for 48 hours at approximately 26 °C. The liver was placed in 60-mL Solo cups (Solo Cup, Lake Forest, Illinois, United States of America) with a layer of distilled water to prevent liver drying and to encourage attractiveness to blow flies inside the traps (Brundage et al. Reference Brundage, Bros and Honda2011), covered by Better Barriers Landscape Fabric (Quest Brands, London, Ontario, Canada) to prevent flies from feeding or ovipositing on the liver bait, and placed inside the RESCUE POP! Fly Traps, per Owings et al. (Reference Owings, Banerjee, Asher, Gilhooly, Tuceryan and Huffine2019). Traps remained at each site for 24 hours, after which the flies were collected, placed in labelled 50-mm Petri dishes, and stored at –20 °C at the Department of Integrative Biology, University of Windsor (Windsor, Ontario, Canada) until identification. Adult Calliphoridae were identified using Marshall et al.’s (Reference Marshall, Whitworth and Roscoe2011) and Jones et al.’s (Reference Jones, Whitworth and Marshall2019) taxonomic keys. Identity of C. stelviana was confirmed by Calliphoridae taxonomist Terry Whitworth (Department of Entomology, Washington State University, Pullman, Washington, United States of America). Voucher insect specimens were deposited in the Forensic Entomology Research Facility collection at the University of Windsor.

Due to cool temperatures, periodic rain, and consistent windy conditions during the sampling period, blow flies were captured at only 13 of the 44 sites. Four C. stelviana adults, all females, were collected from three separate sites. One specimen was collected at Site #15, a high-traffic zone located on the side of County Road 42/Highway 2 in Lakeshore, Ontario (Fig. 1). This site is near a small creek lined with shrubs along the highway. Within this same trap, we also collected four adult Calliphora vicina Robineau-Desvoidy.

Figure 1.

North American regional distribution of Calliphora stelviana (Brauer and Bergenstamm) (Diptera: Calliphoridae) (Whitworth Reference Whitworth2006; Tantawi et al. Reference Tantawi, Whitworth and Sinclair2017; Langer et al. Reference Langer, Kyle, Illes, Larkin and David2019), compared to the location of trap sites that collected C. stelviana in Windsor–Essex County, Ontario, Canada in autumn 2020.

Another adult female was collected at Site #17, a low-density reported roadkill site located within the Municipality of Leamington, Ontario, on the corner of Seacliff Drive and Bevel Line (Fig. 1). This site consisted of shrubbery along the road with a nearby small, forested area. We also collected two C. vicina and two Lucilia sericata (Meigen) (Diptera: Calliphoridae) adults in this trap.

Two adult females were collected at Site #46, a waste zone located along Highway 3 in Leamington that is surrounded by several large greenhouse vegetable operations (Fig. 1). Within the same trap, we collected one L. sericata and four C. vicina adults.

This new record is significant. In forensic entomology, collecting C. stelviana on a homicide victim in a region where this fly has not been previously considered to be native could lead to assumptions about postmortem transfer of the body to southern Ontario from high-elevation areas or more northerly latitudes where C. stelviana has previously been found. This type of information may be critical in a criminal case (Weidner et al. Reference Weidner, Gemmellaro, Tomberlin and Hamilton2017). Our trapping of C. stelviana at sites more than 20 km apart from each other – distances that suggest separate local populations due to other blow fly species having been shown to fly a maximum of 2 km per day (Braack and Retief Reference Braack and Retief1986) – demonstrates that these assumptions need to be approached with caution. Other factors may result in movement of species that have nothing to do with criminal activity but provide windows of dispersal for species’ range expansion or shift, particularly in the face of climate change and extreme weather events.

Andrew and Hughes (Reference Andrew and Hughes2005) have suggested that insect biodiversity will increase in temperate zones in response to climate change shifts. Insects are especially susceptible to changes in their range, life history traits, and behaviours because these are frequently temperature-dependent (Tauber and Tauber Reference Tauber and Tauber1981; Masaki Reference Masaki1983). During the fall trapping period of the present study, the Windsor area experienced 10 days of rain, six days with sustained winds in excess of 29 km/hour (all 24 days had maximum wind gusts greater than 29 km/hour), mean highs of 13 °C, and mean lows of 4° C (Government of Canada Historical Weather Data, Windsor A weather station; https://climate.weather.gc.ca/historical_data/search_historic_data_e.html). Rain (George et al. Reference George, Archer and Toop2013) and winds above 29 km/hour prevent flight by blow flies (Digby Reference Digby1958; Vogt et al. Reference Vogt, Woodburn, Morton and Ellem1983; George et al. Reference George, Archer and Toop2013); however, the flies are capable of flight between wind gusts and periods of rain (Reibe and Madea Reference Reibe and Madea2010), and in more moderate weather, some blow fly species exhibit lower tolerances than others (Lutz et al. Reference Lutz, Verhoff and Amendt2019). The abiotic limits for flight by C. stelviana are unknown; however, given the species’ typical high-mountain or more northerly range, C. stelviana is likely active in cooler weather such as that experienced during the present study’s fall 2020 trapping period in Windsor–Essex County.

Although this cooler weather may be favourable to C. stelviana, those conditions do not explain how the species arrived in southern Ontario. Together with the addition of increased global commerce and trade, movement of plants and wood has been shown to be a key player in the distribution of insect introductions around the world. For example, Fenn-Moltu et al. (Reference Fenn-Moltu, Ollier, Caton, Liebhold, Nahrung and Pureswaran2023) found that the largest interceptions of individuals of the family Diptera were associated with the movement of plant products and of machinery or electrical equipment. Blow flies pupariate in soil such as would be transported with nursery plants and Christmas trees. The province of Québec produces almost 70% of Canada’s Christmas trees and almost 60% of its floriculture and nursery plants for trade within and beyond Canada (Agriculture and Agri-Food Canada 2023). A possible expansion of C. stelviana’s previously documented range in northern Québec southwards into regions of the province where nursery plants are propagated and then are shipped westwards to the Windsor area could explain how the species reached southwestern Ontario, but further research is needed to confirm this hypothesis.