Yes, Female Praying Mantises Do Eat Their Mates

Praying mantises range in size from less than an inch (3 centimeters) to 12 inches (30 centimeters) long. The larger species may live from 4 to 6 months, while the smaller ones live for only 4 to 8 weeks. Most are green, brown or pink and they're great camouflagers, blending in with the type of greenery that surrounds them. And if you're wondering whether a praying mantis will hurt you should you find one in the wild, the answer is no — praying mantises cannot sting and they have no venom. But they'll eat just about anything — worms, other insects, fish and even small birds — but they're not accomplishing these major predatory feats using the usual killer insect playbook. Praying mantises are versatile predators with a unique predatory style.

"Many other predatory insects, like dragonflies, tiger beetles, water boatsmen and robber flies, chase their prey," says Sergio Rossoni, a Ph.D. candidate in the Department of Zoology - Clare College at Cambridge University, and author of a 2020 study about mantids' special predation methods. "On the other hand, mantids try to camouflage themselves, looking like leaves and flowers, and wait for prey to go to them, capturing it if it gets too close."

Mantids are able to sit back and let their quarry come to them for a couple of reasons. For starters, their head is mobile, and their visual system is extremely keen. All predators have to assess their prey's size before they go for it, or else it would be a total waste of time and energy — or worse, the tables could turn, and the predator could become the prey.

"Whilst chaser predators can extract the size of their prey from how big it looks and how quickly it appears to move — if it's big and moves very fast, it's probably a close target, else it'd look smaller and far away — mantids need to make incredibly quick decisions, because they don't chase their prey," says Rossoni. "For this reason, they have evolved two forward-facing eyes and highly mobile necks, much like the flexible neck of owls, so they can direct their gaze in pretty much any direction. Once the prey is in the right portion of the visual field, they can then use their two eyes to triangulate and extract object size and position, much like we humans do with our own eyes."

And mantid eyes are not so different from ours — at least in the way they function. Like us, they use stereopsis, the ability to see the world in three dimensions by comparing images between two eyes, to make sense of what they're seeing. This has always fascinated scientists, and it's long been the main focus of mantid research.

"The underlying assumption was that the visual system of these animals was complex, but the motor commands to capture prey were simple," says Rossoni. "Once prey was visually evaluated and in the right portion of space, the attack was assumed to be stereotypical. Some of the early studies even suggested it could be ballistic, like a chameleon's projectile tongue, and that once initiated, it would carry out automatically."

That is to say, scientists assumed the mantid's eyes did most of the work, and the animal had very little awareness of its actions once the eyes gave the body its marching orders.

"Our study indicates that there's much more to the mantid's strike than originally thought," says Rossoni. "The mantis can transform the visual image of prey approaching into a precisely timed motor program to capture it. Even more surprisingly, mantids are monitoring the prey throughout the attack, as indicated by the fact that they can pause their attack if it's not timed sufficiently well. In the worst case, supposedly when they start attacking too late, we show they can even give up, and abandon the strike altogether. The fact that their nervous system can do these calculations and detect its own mistake is quite remarkable, especially given how fast the attacks are — usually around a 10th of a second."

Mantids are unique, even among their closest relatives. If you look at the family tree of insects, you'll notice that mantids are surrounded by non-predatory relatives. Their closest living relatives are cockroaches, and just as cockroaches do, most adult mantids have wings. While the females usually cannot fly, the males can. They're also closely related to stick insects, crickets and grasshoppers.

"This suggests that they might have unique adaptations that allowed them to evolve as predators, making them a key animal to understand what features are essential for predation, and what are due to evolutionary constraints of a specific predatory group," says Rossoni.

And, because you're dying to know the truth about female mantids eating their mates:

"What people don't know is that this only happens if the female is very hungry and needs energy to develop her eggs," says Rossoni. "But also, it's been shown that if a male has been exposed to the scent of many females, he will try to escape quickly after copulation so as not to get eaten. On the other hand, if the male is only exposed to one female during its lifetime, he will linger around after copulation so that the female might eat him afterwards. To him, being eaten is a better chance of producing surviving offspring, than escaping and dying alone!"