Results
We recorded a total of 86 observations of cannibalism (15 from our field work and 71 from previously published data and web portals). Of them, 32 were in dragonflies and 54 were in damselflies (Supplementary Table 1 & 2). Of the 86 instances, 29-30 incidents of cannibalism involved females feeding on males, 11 incidents involved males feeding on females, 24 incidents showed intrasexual cannibalism (10 cases males feeding on males and in 14 cases females feeding on females), and in 20 incidents adult odonates were feeding on teneral individuals (Supplementary Table 3 & 4; Fig. 2a-b).
In Anisoptera, we found 32 cases of cannibalism in four species under two families. These are Erythemis simplicicollis (n=17),Orthetrum sabina (n= 13) and Orthetrum serapia (n=1) under the family Libellulidae. The family Petaluridae is represented byTachopteryx thoreyi with one instance. On the other hand, in Zygoptera, 51 cases of cannibalism have been recorded in 22 species of damselflies under 12 genera and 4 families. Family Coenagrionidae represents the highest instances of cannibalism (n=50) from 18 species and eight genera, followed by Lestidae (n=2), Calopterygidae and Euphaediae each with one example. In the family Coenagrionidae, the genus Ischnura with 8 species represents 21 cannibalism cases andCeriagrion with 5 species represents 13 examples respectively (Supplementary Table 1 & 2).
Females primarily acted as cannibals. In Anisoptera number of cannibal females was 21 (65.6%) and number of cannibal males was nine (28.1%). In case of Zygoptera we found 26 (48.1%) females as cannibals, followed by 12 male cannibals (22.2%). Based on developmental stage, all the Anisopteran (both predator and prey) involved in cannibalism were mature and young. But in Zygoptera, mature individuals were primarily cannibal and tenerals were primarily (about 44%) target of predation (Supplementary Table 4; Fig. 2).
Our data did not provided evidence that body size of predator (n = 29, mean = 28.6, sd = 6.63) and prey (n = 29, mean = 28.72, sd = 6.72) are different (mean difference = 0.02, 95% CI [-3.16917, 3.54138]) among odonates involved in the cannibalism (Fig 3).