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).