Material and methods
We recorded opportunistic observations of cannibalism in odonates during
field work in India, Bangladesh, and Australia during 2014 to 2024 (Fig
1 a-f). We further collated records of cannibalism from 18 published
literatures (Fraser, 1934; Corbet, 1962; Bick & Bick, 1963; Bick &
Sulzbach, 1966; Müller, 1972; Martens & Smeyer, 1978; Utzeri, 1980;
Robinson, 1983; Robertson, 1985; Fincke, 1987; Dunkle, 1990; Cordero,
1992; Rolff & Kröger, 1997; Reels, 2010; Nair, 2011; Kosterin &
Chartier, 2017; Payra, 2020; Priyadarshana, 2021) , peer-reviewed web
portals (http://www.odobd.org,
https://www.indianodonata.org) (Shah & Khan, 2020; Joshi et al.,
2022), and observation of community scientists in online platform
https://www.inaturalist.org/, and taxonomy focused social media group
(http://www.facebook.com/groups/OdoBD).
After accumulation of photographic records and observations, we
identified the species, life stages (adult, immature, and teneral), and
sexes (male, female) of the involved individuals by using taxonomic keys
of Fraser (1933, 1934, 1936), Abbott (2015), Boudot et al.(2021) and
peer-reviewed websites
(http://www.odobd.org and
www.indianodonata.org) (Shah &
Khan, 2020; Joshi et al., 2022). Based on the life stage and sex
involved individuals were categorized as Mature Male (m♂), Mature Female
(m♀), Young Male (y♂), Young Female (y♀), Teneral Male (t♂), and Teneral
Female (T♀). Body size (average length of abdomen including appendages)
of involved males and females in cannibalism was obtained from Fraser
(1929, 1933, 1934, 1936); Rodrílguez et al. (2015); Boudot et al. (2021)
and the website (http://www.odobd.org ). We applied DurgaDiff
function of Durga R package v2.0 (Khan & McLean, 2024) to determine if
there is difference of body size between predator and prey of
individuals involved in cannibalism. The likely mechanisms of
cannibalism in adult odonates were categorized in three categoriesviz ., Female driven cannibalism (Females cannibalizing males),
male driven cannibalism (males cannibalizing females), intrasexual
cannibalism (when males devouring males and females devouring females).
We used 63 (28 Anisoptera and 35 Zygoptera) out of 83 observations where
we could identify the sexes based on the photographs and literature, to
determine the involvement of the sex in cannibalism. Further to
ascertain the involvement of life stages in cannibalism we choose 73
instances (30 Anisoptera and 43 Zygoptera) where we were able to
identified the life stages confidently. Instances where we could not
identify age or sexes correctly were removed from the final analysis.