Description of the larva of Vestalis gracilis (Rambur, 1842) (Zygoptera: Calopterygidae) from Thailand

Vestalis gracilis (Rambur, 1842) is a forest stream damselfly belonging to the family Calopterygidae. Its last-stadium larvae and exuviae are described and illustrated based on laboratory-raised specimens from Thailand, and observations of agonistic behavior are provided. The taxonomical characters of V. gracilis larvae are similar to those of V. amoena. They exhibit synapomorphic characters such as posterlaterally directed protuberances on the postocular lobes, posterior margin of median lamella obliquely truncate, and two setae on labial palps. Vestalis gracilis and V. luctuosa bear eight antennal segments whereas seven antennal segments are found in V. amoena. The most significant difference between V. gracilis and V. luctuosa is that V. luctuosa has posterolaterally directed protuberances on the postocular lobes and an obliquely truncate posterior margin of the median lamella.