Praying Mantis- Are they good for the garden?
You often see egg cases of praying mantis for sale in garden catalogs and some gardeners believe that the little creatures are the answer for problem insects in the garden. But are praying mantises really beneficial for the garden? Most entomologists would tell you their presence in the garden is neutral- the benefits are erased by the costs.
Praying Mantis should really be called preying mantis, because they do far more preying than praying. These odd-looking creatures are the source of folklore around the world and are even kept as pets. There are several native species of mantis, the most common being the Carolina Mantis, (Stagmomantis carolina) which is found throughout most of the eastern half of the US and even south into Mexico. The European mantis (Mantis religiosa), and the Chinese mantis (Tenodera sinensis), were introduced into North America with the hope they would clear out garden and crop pests. Both of these species are fairly common across most of the US and all species are called by the common name Praying Mantis.
A mantis has a large head shaped like a triangle with a distinct “snout”. There are two large prominent compound eyes and 3 small simple eyes most people don’t notice. The head also has 2 antennae. Most mantis species have a flexible neck and can rotate their heads almost 180 degrees.
Mantis have 2 large forelegs, with spikes and a claw at the end that allow them to firmly grasp their prey. They also have 2 other sets of legs close together in the middle section of their body. (Like most insects there are 3 segments to the body.) Mantis have long bodies that are slimmer in males and in both sexes end in 2 cerci, tail like appendages many people think of as “pinchers”. Females usually are larger with plumper abdomens. The Carolina Mantis can be 3-4 inches long.
All of the common mantis species mentioned have 2 sets of wings, an outer tough, colored set and an inner, thin almost clear set. Once adult, mantises don’t do a lot of flying, especially the heavy females. Mantis colors range from brown to green and tend to match the surroundings, so they blend in and are camouflaged from their prey and things that might prey on them.
The Carolina mantis can be brown or green. The wings of the male reach to the end of the body, while those of the female end about ¾ of the way down the body. The females of this species are very large and plump when mature. The European mantis is usually green, with distinctive black spots on the underside of the first body segment (chest), some of which may have a white center. The Chinese mantis is usually slimmer and smaller than the other two. It can be either brown or green but has a light green stripe running along the edge of the outer wings. It can be difficult to tell the species apart, especially when they are young.
Praying mantis are predators, eating all kinds of insects and even small frogs, toads, lizards and the occasional small bird, like hummingbirds. Usually they lay in wait for their prey, moving with remarkable speed when the victim is close enough to grab. Sometimes however they stalk their prey, moving slowly and carefully until they are close enough to grab it. They usually begin munching the head of the victim first. They have strong mandibles (jaws) to crush insect shells.
Praying mantis can bite a human if provoked, but it’s not poisonous, is only a tiny prick and won’t happen if you leave them alone. You cannot catch diseases from a mantis and they will not attack you. The old wife’s tale that mantis can spit into your eyes and blind you is just that, an old wives tale. While mantis may produce some brown discharge from the mouth when scared, they don’t spit and the discharge won’t harm you.
Because they do not specialize in any type of insect praying mantis also eat many beneficial insects including bees and butterflies which is why most experts consider their status neutral for pest control. For every pest insect they consume they probably consume a helpful insect too. They also eat each other so you usually won’t find many mantises in the same area. When people buy egg cases to hatch out in the garden, many mantises may hatch and then turn on each other, leaving only a few in the garden.
Praying mantises are also eaten by other things, birds, frogs, and small mammals. When attacked they often stand up their back legs, spread their wings and wave their front legs in an effort to look larger and intimidate their enemy.
Praying mantises live about 1 year, one season in colder areas of the country. Mating season is in late summer- early fall. Yes, female mantises may eat the smaller males when they mate. But it’s not as common in nature as the stories would suggest. In captivity cannibalism during mating is about 90% but researchers found that in nature the odds of a male being eaten during any single mating are only about 25%. However, since males generally mate with several females their odds of escaping death during the mating season are probably low.
After mating females lay eggs that stick to objects like twigs, posts, and garden ornaments. They then produce a brown foamy substance that covers the eggs and quickly hardens into a protective case. (I think it looks like the foam stuff you spray into cracks that expands and hardens to seal them.) In cold climates the eggs don’t hatch until warm weather in the spring. Egg cases are called ootheca. You can collect and move them to the garden and they will be fine.
Eggs hatch into mantis nymphs, wingless but looking like small versions of the adults, and then rapidly become winged adults. Praying Mantises usually don’t fly far from where they hatched. But because they consider each other food, only a few mantises will survive from any egg case you place in the garden.
Praying mantises are fascinating to observe in the garden but in reality they probably won’t do much to control insect pests since only a few will be able to co-exist in the garden. If you see one around your hummingbird feeder I would remove it to another part of the garden. I have heard bee keepers complain that they sometimes hang around hives to eat bees. Buying several egg cases for the garden is probably wasted effort but it can be fun for children to watch the insects hatch and catch their prey.