Mantises have two grasping, spiked forelegs ("raptorial legs") in which prey items are caught and held securely. The first thoracic segment, the prothorax, is commonly elongated and flexibly articulated, allowing for greater range of movement of the front limbs, while the remainder of the body remains more or less immobile
The articulation of the head is also remarkably flexible, permitting nearly 300 degrees of movement in some species, allowing for a great range of vision (their compound eyes have a large binocular field of vision) without having to move the remainder of the body. As their hunting relies heavily on vision, they are primarily diurnal, but many species will fly at night.
Mantises are exclusively predatory. Insects form the primary diet, but larger species have been known to prey on small scorpions, lizards, frogs, birds, snakes, fish, and even rodents; they will prey upon any species small enough to successfully capture and devour.
Most species of mantis are known to engage in cannibalism. The majority of mantises are ambush predators, waiting for prey to stray too near. The mantis then lashes out at remarkable speed. Some ground and bark species, however, pursue their prey. Prey items are caught and held securely with grasping, spiked forelegs.
Generally, mantises protect themselves by camouflage and concealment. When directly threatened, many mantis species stand tall and spread their forelegs, with their wings fanning out wide. The fanning of the wings makes the mantis seem larger and more threatening, with some species having bright colors and patterns on their hind wings and inner surfaces of their front legs for this purpose
If harassment persists, a mantis may strike with its forelegs and attempt to pinch or bite. As part of the threat display, some species also may produce a hissing sound by expelling air from the abdominal spiracles.
When flying at night, at least some mantises are able to detect the echolocation sounds produced by bats, and when the frequency begins to increase rapidly, indicating an approaching bat, they will stop flying horizontally and begin a descending spiral toward the safety of the ground, often preceded by an aerial loop or spin
Mantises, like stick insects, show rocking behaviour in which the insect makes rhythmic, repetitive side-to-side movements. Functions proposed for this behaviour include the enhancement of crypsis by means of the resemblance to vegetation moving in the wind. However, the repetitive swaying movements may be most important in allowing the insects to discriminate objects from the background by their relative movement, a visual mechanism typical of animals with simpler sight systems
Sexual cannibalism is common among mantises in captivity, and under some circumstances may also be observed in the field. The female may start feeding by biting off the male's head (as they do with regular prey), and if mating had begun, the male's movements may become even more vigorous in its delivery of sperm. Early researchers thought that because copulatory movement is controlled by a ganglion in the abdomen, not the head, removal of the male's head was a reproductive strategy by females to enhance fertilisation while obtaining sustenance. Later, this behavior appeared to be an artifact of intrusive laboratory observation.