There’s no mistaking a praying mantis! Praying mantises are named for the front-facing, folded forelegs that give the appearance of an animal in prayer. Really, though, the series of spikes along those “arms”, along with their lightning-fast movements, are a major element of the mantis’s success as a fearsome predator. “Preying” mantis, perhaps?
Praying mantises are members of the insect order Mantodea. There are nearly 2,500 species of mantises worldwide. Oddly, though, just a single species is native to Ohio. By comparison, Ohio is home to approximately 150 species in the order Odonata (dragonflies and damselflies) and something like 3,000 in the order Lepidoptera (about 150 species of butterflies, the rest moths). Our one native mantis is the Carolina mantis, Stagmomantis carolina.
Carolina mantises present all the standard mantis features. Mantises hatch out of the egg as nymphs, basically miniature versions of the adult, though without wings. They are predatory from day one, though the size and identify of their animal prey changes as they grow. Contributing to that predatory prowess, praying mantises have large, laterally placed eyes that generate high resolution, stereoscopic vision. Along with a head that swivels through 180 degrees, mantises can track prey without moving their body. So, praying mantises adopt a “sit and wait” hunting strategy, pouncing on any potential prey that wanders within reach. Mantises mostly eat arthropods — grasshoppers, flies, bees, butterflies, spiders, etc. — but they might occasionally grab a small frog, lizard, or other animal. Larger mantises (not Carolinas) have even been known to capture unsuspecting hummingbirds.
From a human (and maybe insect prey!) perspective, mantis predation is rather horrific. As noted above, mantises have extremely fast reflexes, and their serrated forelegs create an inescapable grip. The consequence is that mantises do not need to further subdue their prey; there is no stinger, no venom, no death blow. The mantis simply holds on while it devours its prey, one small bite at a time. The unfortunate victim eventually dies during the process.
Although the Carolina mantis is Ohio’s only native mantis, a few other species have been introduced to the state. One of those — the Chinese mantis Tenodera sinensis — is probably more common and more often encountered than the Carolina mantis. The two species are relatively easy to distinguish. Both are colored some combination of green and/or brown, but the Carolina version is smaller (5 vs 10+ cm in length as adults), has shorter wings (typically failing to extend to the end of the abdomen), and lacks the striped facial markings characteristic of the introduced species.
Adult female Carolina mantises lay eggs in the fall, forming a flattened egg case (ootheca) that hardens to a Styrofoam-like consistency. Adults do not survive the first hard frosts of autumn, but the egg case overwinters and babies emerge in late spring. Hatching success and survival of juveniles can be low, and hatchlings grow slowly, so relatively few eggs end up producing new adults by late summer. Their smaller size also makes them more vulnerable to predators than the larger introduced species. Together, all these factors create the generally low population densities of Carolina mantises.
Two aspects of mantis biology are widely held but open to question. The first is that the female mantis consumes the male during mating. It is true that mantises (both male and female) are fairly non-selective predators; they will eat anything they can catch, including sometimes other mantises. Moreover, female mantises are larger than males and so have the advantage as predators. Nevertheless, while sexual cannibalism has been observed occasionally in captive Carolina mantises, it remains unclear how often, if ever, it occurs in the wild.
A second holding about mantises is that they exert significant impact on the diversity and/or amount of insect life in their habitat. In other words, it seems reasonable to suspect that mantises are effective enough predators that they reduce the abundance of other insects. However, actual evidence for that impact is not compelling. Studies of Carolina mantises have found little effect on other insect populations. Perhaps that is because of the low density of Carolina mantis populations. However, even the larger, more abundant Chinese mantises may, by themselves, have relatively low impact on their insect communities. Clearly, many other factors, including other insectivores, are important, too.
That ambiguity about the impact of predation by mantises applies to a more practical setting as well. Mantis egg cases (usually of Chinese mantises) can be purchased commercially, and it is not uncommon for home gardeners to place them among the plantings, hoping they will suppress insect pests. That might be true — but mantises are just as likely to prey on beneficial insects, including a variety of pollinators. So, the net benefit of “mantis supplementation” remains an open question.
Be that as it may, mantises never fail to intrigue. Give one a long look and those big eyes will return the stare right back! September is the optimal time to find mantises among the late season wildflowers. Be on the lookout!
Article and photo contributed by Dr. David L. Goldstein, Emeritus Professor, Department of Biological Sciences, Wright State University.