Cannibalism (zoology)

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Three Mormon crickets eating a fourth Mormon cricket

In zoology, cannibalism is a common ecological interaction in the animal kingdom and has been recorded for more than 1500 species (this estimate is from 1981, and likely a gross underestimation).

Sexual cannibalism has been recorded in the female red-back spider, black widow spider, praying mantis, and scorpion, among others. In this form of cannibalism, the female sometimes eats the male after mating.

The more common form of cannibalism is size structured cannibalism, in which large individuals consume smaller conspecifics. In such size-structured populations, cannibalism can be responsible for 8% (Belding Ground Squirrel) to 95% (dragonfly larvae) of the total mortality, making it a significant and important factor for population and community dynamics. Such size structured cannibalism has commonly been observed in the wild for a variety of taxa, including octopus, bats, toads, fish, monitor lizards, red-backed salamanders and several stream salamanders, crocodiles, spiders, crustaceans, birds (crows, Barred Owls), mammals, and a vast number of insects, such as dragonflies, diving beetles, back swimmer, water strider, flour beetle, caddisflies and many more.

Unlike previously believed, cannibalism is not just a result of extreme food shortage or artificial conditions, but commonly occurs under natural conditions in a variety of species. In fact, scientists have acknowledged that it is ubiquitous in natural communities. Cannibalism seems to be especially prevalent in aquatic communities, in which up to ~90% of the organisms engage in cannibalism at some point of the life cycle. Cannibalism is also not restricted to carnivorous species, but is commonly found in herbivores and detritivores.

Another common form of cannibalism is infanticide. Classical examples include the chimpanzees where groups of adult males have been observed to attack and consume conspecific infants, and lions, where adult males commonly kill infants when they take over a new harem after replacing the previous dominant males.