Capture-Mark-Release (Mark-Release-Recapture) Records of Rainbow Scarabs (Phanaeus vindex) from Two Farms in SE-Michigan

Until now, little is known about the population structure and mobility of temperate dung beetles including the rainbow scarab Phanaeus vindex (MacLeay 1819) although this knowledge is essential for their conservation as pastures become increasingly rare and the landscape fragmented by monocultures and urbanization. Here, we estimate population size, longevity, and dispersal within and between pastures. For three years, we life-trapped beetles every week on 2 adjacent farms in SE-Michigan, determined their sex, male morph, and size, and marked their elytra with individual tattoo patterns before releasing them. We marked a total of 470 rainbow scarabs of which 14 were recaptured once and two were recaptured twice. The sex ratio was not significantly sex-biased but fluctuated between months with no apparent uniformity between years. While the minor to major male ratios were unbiased in 2019 and 2020, they were marginally minor-biased in 2021. The gross population estimates for the two farms were 458-491 and 217 rainbow scarabs, respectively. Beetles travelled distances of up to 178 m within farms. No beetles dispersed between farms. One large female was recaptured after 338 days documenting the first cold hardiness and long lifespan of a cold-temperate dung beetle species. The low population estimates on both farms indicate two vulnerable populations with no or extremely limited connectivity. Supplementary funding for the land stewardship of small-scale cattle farmers could stabilize populations of native dung beetles and maintain their ecosystem services.