An investigation of carrion beetle (Coleoptera: Silphidae) swimming endurance and immersion tolerance as it relates to standard trapping protocol

Carrion beetle (Coleoptera: Silphidae) populations are monitored throughout the known range of the federally endangered American burying beetle, Nicrophorus americanus. The standard trapping protocol utilizes a pit-fall trap baited with a rotten meat; during periods of heavy rainfall, traps can flood and have been suggested to result in burying beetle mortality. In this study, the swimming endurance and immersion tolerance of two carrion beetle species, Nicrophorus marginatus (Fabricius) and Necrodes surinamensis (Fabricius), were examined. Both species exhibited swimming endurance well beyond the standard length of time in which traps are checked and rebaited. Total swimming time of Nicrophorus marginatus (n=30) and Necrodes surinamensis (n=30) were 71.4 ± 48.4 hours (mean + 1 S.E.) and 116.4 ± 45.6 hours, respectively. However when individuals were immersed, survival times were less than 8 hours and 1 hour respectively. These data suggest carrion beetle mortality is not caused by drowning via flooded spiracles but rather hypoxic conditions created by the pit-fall trap. Immersed beetles initially appeared dead and recovered over a period of hours. During field sampling, beetles including N. americanus found in flooded traps should be retained in moist soil conditions for at least 4 hours prior to assuming mortality.