The rainbow scarab Phanaeus vindex is native to North America and provides substantial ecosystem services to pasture systems. Until now, little is known about its population size, sex ratio, male minor/major ratio, and mobility. This information is urgently needed for the species’ conservation as pastures become increasingly rare and the landscape is fragmented by urbanization. Here, we provide some of these data and estimate the population size, viability, and the beetles’ mobility within a pasture. For two years, beetles were trapped alive every week using ten life pitfall traps set for 24h. Beetles’ elytra were marked with individual tattoo patterns using a small nail drill. We captured a total of 238 rainbow scarabs comprising of 124 females and 114 males, which is not significantly different from a balanced sex ratio of 0.5 (c2 (1, N=238) = 0.517, p < 0.5). The sex ratio changed over the months with more males than females captured in August and vice versa in the other sample months (not/marginally significant). Of the 114 males, 52 were major and 62 were minor morphs. Male minor/major ratio fluctuated throughout the year but only August 2020 was marginally minor-biased (p=0.07). In 2019, we recaptured two of 108 beetles and in 2020 six of 130 beetles. Beetles were recaptured after 7-22 days and travelled up to 178 m between release and recapturing locations. The low number of recaptures indicates either a large population, substantial mobility, or high mortality – or a combination of these factors.
