Why Do Female Praying Mantises Eat Males? Mating Cannibalism

How often do female mantises eat males?

Sexual cannibalism means eating a partner before, during or after mating. In mantises it was first described from insects kept in jars and cages, where hungry females often ate the males placed with them. For decades many scientists suspected it was mostly a side effect of captivity.

Field studies changed that view. A 1992 study of the European praying mantis, published in Animal Behaviour, watched mantises in the wild and found cannibalism in roughly a quarter to a third of the pairings observed. Studies of the Chinese mantis in North America found that most males escape any single encounter, but because males may mate more than once, their total risk adds up over a season.

Captivity can still exaggerate the numbers. Mantises are very visual animals and react to bright lights and moving observers. In the 1980s, researchers who filmed well-fed Chinese mantises without disturbing them recorded elaborate courtship displays, in which the male seemed to shift the female’s attention from feeding to mating.

Why do female mantises eat males?

The simplest answer is that a female mantis is an ambush predator that grabs almost any moving animal of the right size. A male that comes within reach looks a lot like prey, and he is often bigger than anything else she could catch that day.

Hunger is the strongest trigger. Females on poor diets are much more likely to attack males, and starved females may even eat a male before mating starts. Late in the season, when insects become scarce and a female is building a large egg case, a meal of male mantis is valuable.

Experiments show the meal really pays off for the female. In the false garden mantis (Pseudomantis albofimbriata) of Australia, females that ate males grew into better condition and laid more eggs. A 2015 study of the same species found that very poorly fed females attracted more males than better-fed ones, probably through their scent. Researchers called this the “femme fatale” effect: hungry females advertise themselves and then eat some of the males that arrive.

Can a male mantis mate after being eaten?

A female usually starts on a male the way she starts on any prey, by eating the part closest to her jaws, which is often his head. Remarkably, this does not stop mating.

In the 1930s, experiments with the European mantis showed that the movements of mating are controlled by nerve centers in the male’s abdomen rather than his brain. A headless male can therefore keep mating, and in some cases his movements become even more vigorous. Some studies have found that mating lasts longer when the male is being eaten, which may allow him to transfer more sperm.

Does being eaten help the male?

Biologists have long wondered whether a male that is going to die anyway gains something from becoming a meal. A 2016 study of Chinese mantises tested this with radioactively labeled crickets. The eggs of females that ate their mates contained significantly more material from the male’s body than the eggs of females that did not, and cannibalistic females went on to lay more eggs.

So a male that is eaten does contribute directly to his own offspring. Even without cannibalism, the same study found that males passed about a quarter of their labeled amino acids to females during mating.

That does not mean males volunteer. A living male can try to mate with other females, and almost everything about male behavior shows that being eaten is something to avoid.

How do male mantises avoid being eaten?

Male mantises use a whole set of survival tactics:

• Slow approach. A male usually creeps up from behind and freezes whenever the female turns her head. Because mantises spot movement far better than still objects, this stop-and-go stalk can take hours.
• Good timing. Males approach faster and more often when the female is busy eating or cleaning herself. In the East Asian mantis Tenodera aridifolia, males make their approach when wind stirs the vegetation and masks their movements.
• Extra caution with hungry females. In the Chinese mantis, males approach hungry females more slowly and stay mounted on them longer, apparently waiting for a safer moment to leave.
• A careful exit. Dismounting is the most dangerous moment, so males leave quickly once they let go. European mantis males have been seen dropping off and freezing about 50 cm (20 in) from the female before leaving.
• Wrestling. In the springbok mantis (Miomantis caffra), a 2021 study found that males and females wrestle when they meet. When the female grabs first, she eats the male. When the male grabs first, his chance of mating rises sharply.

Is sexual cannibalism unique to mantises?

No. Sexual cannibalism is also known in some spiders, including widow spiders and some orb-weavers, and in a few other insects. In the Australian redback spider, males even flip their bodies toward the female’s jaws during mating. Mantises are simply the most famous example, partly because they are large, common and easy to watch.

For a mantis, a male is just one more item on a broad menu, explained in what praying mantises eat. For people, mantises remain completely harmless, as described in do praying mantises bite?