Observations on Aphrodite Fritillaries (Argynnis aphrodite) at Roxborough State Park, Colorado

Life history information of a common Roxborough State Park (SP) butterfly, Argynnis aphrodite Fabricius 1787, is limited at Roxborough SP and the surrounding region. While abundant in most years at the park, this species has been negatively impacted via climate change in other parts of the United States (e.g., Wepprich et al. 2019). Study of Roxborough A. aphrodite populations provides an opportunity to obtain data where abundance is relatively high and perhaps offers clues for impact amelioration elsewhere. I present information on phenology, sex ratios, behavior, wing size, weight, and response to weather of A. aphrodite in Roxborough SP over the years 2018 to 2024. Unusual results included the presence of what appeared to be newly emerged individuals (based on a wing damage metric) of both sexes throughout the entire flight period; including in August/September several months after literature suggests they have initially eclosed. It appears, in the case of females, that they remain hidden and limit flying in the environment until post-summer aestivation, thereby retaining their excellent appearance into September. Mostly males are seen in June/July and egg laden females dominate in August/September. The majority of adult males likely perish by the end of their flight in July, leaving the environment to females in August/September, with the exception of a few late season males. The use of wing damage metrics as an indicator of butterfly age probably has value for males but, because of limited flying, is not necessarily valid for females. Observed behaviors also differed between pre- and post- aestivation and were mostly linked to important male vs. female requirements. Data collected on sizes of A. aphrodite found females to be statistically heavier and with greater forewing length than males. Anomalous spring time weather in 2023 appeared to dramatically decrease A. aphrodite abundance, and low abundance may have affected behavior. Weather may have delayed timing of female emergence. Searching for females (fleeking), a dominant male behavior in 2022, was not observed in 2023. Abundance was also low the following year, in 2024. Argynnis aphrodite populations seemed to be very responsive to a variety of weather effects. I present a diagram of A. aphrodite life history stages associated with Roxborough SP and perhaps other locations.