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.