It's an esoteric debate that sometimes erupts among organic gardeners: Are praying mantises good bugs or bad bugs? The question is irrelevant, even inane, says Dan Digman, an entomologist at Ohio State University. Mantises (also known as mantids) are predators—pure and simple. If hordes of Mexican bean beetles are defoliating your wax beans, you can bet that nearby mantises will be munching beetles. But if a tasty lacewing or honeybee flies within snagging distance, don't expect a mantis to pass up such an easy meal. To a mantis, all bugs are good bugs—good to eat, that is.
"Generally, mantises are good for the garden. They're part of a solution to a pest problem," says Digman. "But they eat beneficials, too. And if nothing else is available, they'll eat each other."
Warm-Weather Beasts Mantids are warm-region insects. Although 1,800 species exist worldwide, only 11 are found in North America. The Carolina mantis (Stagmomantis carolina), which is widespread through the South, and the obscure ground mantid (Litaneutria obscura), common in the Great Plains and arid West, are American natives. But the Chinese mantis (Tenodera aridifolia sinensis) and the common European mantis (Mantis religiosa) were both introduced to the Northeast for insect control. All are known by the common name praying mantis.
Praying for Prey When lying in ambush for prey, all mantises strike the same "prayerful" posture of folded front legs held tight to the body. They use their back and middle legs to grasp a twig or stem. When an insect comes into reach, the mantis strikes out, impales, and holds the prey with its spiny, or toothed, front legs. The strike occurs in the blink of an eye. A Carolina mantis can actually strike twice before a housefly can open its wings to attempt an escape.
Chowing Down Voracious is the word that best describes mantids' appetites. They eat caterpillars, butterflies, flies, bees, wasps, and moths. Big mantids in the tropics take lizards, hummingbirds, and small frogs. Praying mantises hunt during the day and night. Frequently, they position themselves near porch lights and streetlights to capture moths and other night-flying insects. "They are just programmed to eat. It's what they do," Digman says.
Camouflage Mantids are big, slender insects; they're 2 to 4 inches long when fully grown. Ranging from green to brown in color, they blend in well among grasses and shrubs. They're found in fields, pastures, ditches, and gardens. In temperate climates, mantids hatch in spring, mature by late summer, and die with the onset of cold weather.
Finding Egg Cases Each fall, females deposit eggs in frothy brown cases that they attach to twigs. The cases harden, protecting the eggs from birds and weather. If you find them, you can remove the egg cases and put them into your garden. Or you can buy egg cases from beneficial-insect suppliers. The mantids aren't pets, however, and it's unlikely that they'll hang around your garden long after hatching, says Digman. "Unless you have a lot of bugs in your garden, mantids will move on," he says. "They need to eat."
Swivel Heads The ability of mantids to cock their heads from side to side and even look backward is unique among insects. This dexterity and their large compound eyes and muscular mouthparts, which can crack open the armor of many insects, give mantids a fearsome, unsettling appearance, but they are harmless to humans. They neither bite nor sting. They seem fearless, as well. When approached by a bigger animal, mantids will rear up on their back legs and extend their wings to appear more threatening—hence their given folk name, "rear-horse."
Sex to Die For Cannibalism is common among mantids. After hatching, the young will eat one another if they don't immediately find prey. The adult female may consume her own mate, severing the male's head while the pair are in the act of copulation.
"Severing the head does a couple of things. It actually stimulates the male to copulate and keeps him there so he remains in the act. And it guarantees the female that the male is not going to eat her first," Digman says.
Love-hungry males inherently understand the risk of this rough sex and will try to take the females by surprise and jump away immediately after mating.