Cannibalism in adult odonates (dragonflies and damselflies): an intriguing but unexplored behavior

Several insect groups exhibit the phenomenon of cannibalism, preying upon individuals of the same species. Cannibalism is an intriguing behavior but often poorly understood. Cannibalism is thought to be influenced by the sex, life history stage, and physiological condition as well as ecological and social contexts in which it occurs. Here we review cannibalism in a carnivorous insect order Odonata (dragonflies and damselflies), on the adult stage of their life cycles, based on primary and secondary data. We collected primary data from our field work (mostly from opportunistic observation) spanning eight years from three countries (India, Bangladesh and Australia) and secondary data including published literature and observations from global citizen science portals. In total, we retrieved 86 instances of cannibalism and metadata (developmental stage and sex of the individuals involved in cannibalism) of 63 cannibalistic instances. We found that, Odonata families with most reported cannibalism cases were Coenagrionidae (n=50) and Libellulidae (n=31) followed by Lestidae (n=2), Aeshnidae, Calopterygidae and Euphaediae each with one example. We classified the cannibalism in odonates into four patterns, 1) Females cannibalizing males, 2) males cannibalizing females, 3) intrasexual cannibalism and, 4) mature individuals cannibalizing tenerals. We found, female cannibalizing males was higher in proportions, compared to males cannibalizing females, and intrasexual cannibalism. We further found that, individuals involved in Anisopteran cannibalism were mostly matures, but in case of Zygoptera, mostly matures individuals were canabilising tenerals. We discuss that species recognition errors, intrasexual competition for mating, and mating harassment avoiding strategies are major driving factors of cannibalism in odonates. We provide a comprehensive insight into the cannibalistic behavior of adult odonates and highlight that experimental evidences are required to understand the mechanisms of cannibalism.