Evaluating exuvia collection as a management tool for the federally endangered Hine’s emerald dragonfly, Somatochlora hineana Williamson (Odonata: Cordulidae)

Reliable population density estimates are crucial for monitoring endangered species. Many species are difficult to capture or range over large areas, making direct monitoring of populations through capture or observation extremely challenging. In such cases, indirect methods of assessing populations can be the only source of reliable information. We examined whether the discarded exoskeleton of the last larval instar (exuvia), left behind when dragonflies emerge into the adult stage, could be used to predict larval densities and provide life history information for the federally listed endangered, Hine’s Emerald Dragonfly ( Somatochlora hineana). Using standardized protocols, we collected exuvia within six 2 × 2 m plots in an ephemeral wetland in Door County, Wisconsin during spring and summer of 1999 and 2000. S. hineana is a “summer emerger”, with more than 95% of the emergence occurring from late June until mid-July. Based on time of emergence and the flight period, adults appear to live a month or longer. The sex ratio at emergence did not differ significantly from a 1:1 ratio and emergence was synchronous between the sexes. Estimates of larval population density using exuvial data were similar to those obtained through intensive direct sampling for larvae. Exuvial collections provide a reliable estimate of larval population density, help link larval ecology to adult ecology and are a useful tool for assessing habitat suitability. Although sampling exuviae requires repeated searching on particular sites, less expertise and fewer people are required for this type of sampling, indicating that exuvial surveys can be a very effective tool for monitoring populations of endangered dragonflies.