Introduction
Cannibalism, the phenomenon of killing or consumption of conspecifics, is an intriguing behavior. The behavior can have negative consequences to the fitness of a population by means of cannibal acquiring pathogens from its prey as well as getting injured by the intended prey of similar size (Elgar & Crespi, 1992; Dhandapani et al., 1993; Williams & Hernandez, 2006; Richardson et al., 2010). However, cannibalism, can maintain population density, reduce competition, and provide essential nutrients to the conspecific predator (Elgar & Crespi, 1992; Richardson et al., 2010).
Cannibalism has been recorded in wide taxonomic groups (Fox, 1975; Polis, 1981) from bacteria, protozoa to invertebrates and vertebrates (Mitchell & Walls, 2008). Among the invertebrates, insect orders including, Hemiptera, Mantodea, Neuroptera, Lepidoptera, Orthoptera, Thysanoptera, Trichoptera, Blattodea, Diptera, Coleoptera, and Hymenoptera, exhibit cannibalism across different life stages (Capinera, 2008; Richardson et al., 2010). These intraspecific predations can be seen between adult individuals (such as in spiders, Odonates, Orthoptera, and Blattodea), between adult and immature (Coleoptera), between larvae (Hymenoptera, Lepidoptera, Diptera) as well larvae and adults predating on eggs and pupae (Lepidoptera, Coleoptera, Blattodea) (Capinera, 2008; Richardson et al., 2010).
Odonata are one of the most successful carnivorous insects (Corbet, 1999). One of the earliest observations of cannibalism in adult odonates was reported in Euphaea dispar (Rambur, 1842) by Fraser (1934). Since then, cannibalism has been reported to occur across larval and adult stages in odonates (Utzeri, 1980; Corbet, 1999; Ilmonen & Suhonen, 2006). Cannibalism in larval odonates was predicted to occur due to high population density, low food resource, difference in population size structure and seasonal time constraints (Fincke, 1994; Sniegula et al., 2017). However, experimental evidence behind cannibalism in adult odonates is still unclear. A few hypotheses have been suggested explaining cannibalism in odonates by various researchers. In Zygoptera (damselflies) cannibalism might be an act of predation that takes place due to failed intraspecific communication (Utzeri, 1980). Intraspecific predation usually involves mature adults predating on tenerals, which are unable to perform threat display (Corbet, 1999). Females may consume males due to lack of intraspecific recognition and lack of proper response to the threat displayed by males (Cordero, 1992). Environmental conditions such as low temperature may also drive cannibalism (Rolff & Kroger, 1997).
Previously published literature documented cannibalism of adult odonates mostly in Zygoptera, whereas cannibalism in Anisoptera (dragonflies) remained overlooked till date. Furthermore, the lack of systematic data collection and compilation in Odonata make it difficult to understand the prevalence of cannibalism and its underlying ecological and evolutionary driver. Here, we provided our observations of cannibalism in adult odonates and also reviewed the occurrence of cannibalism in dragonflies and damselflies from the published literature. We aim to determine taxonomic distribution of cannibalism, involvement of life history stages, and the most likely mechanism of cannibalism in adult odonates.