Conservation Outdoors

The Observant Gardener: Praying Mantis … Friend or Foe?

From whence arrived the praying mantis? From outer space, or lost Atlantis? ­— Ogden Nash

By Judith Canty Graves

Praying Mantis. Photo by Judith Canty Graves

I have always considered the praying mantis to be a beneficial insect that helps control pests in my garden. They have voracious appetites and eat whatever they can, including many garden pests such as wasps, mosquitoes and flies.

But in recent years I’ve read articles about two types of praying mantises: the Chinese mantis, which is not native to the US but originated in Asia; and the Carolina mantis, a species native to the Southeast. Most of us have probably never seen a Carolina mantis because the larger, more aggressive Chinese mantis has largely replaced the native species since its accidental introduction to the US in 1895.

There are differences between the two. The most obvious is size. The Chinese mantis can grow as large as five inches, while the Carolina mantis is rarely larger than three. Another difference is the size and shape of the egg case, called an ootheca. Chinese mantis egg cases are described as resembling “tan toasted marshmallows.” The Carolina mantis ootheca is smaller and elongated with a smooth surface and brown stripes. But, perhaps the most notable difference is the greater predatory skill of the Chinese mantis.

There is some controversy about whether the Chinese mantis is an invasive pest. The US Department of Agriculture does not think so, but many conservation groups disagree. Since the mantis hunts around flowering plants during summer and fall, it eats many beneficial pollinators such as honeybees and butterflies. The Chinese mantis also eats the smaller Carolina mantis and has been known to eat small reptiles, amphibians and even hummingbirds. This was distressing for me to read! After finding the remains of several swallowtail butterflies in my yard last summer, I decided to do something.

Last November, after I found 32 Chinese mantis egg cases in my yard, I threw the cases into a pond, as recommended on a website about invasive species. Even though not all newly hatched mantises survive, these egg cases represented possibly hundreds of adult mantises. Next, I ordered three Carolina mantis egg cases.

Following the instructions, I kept them indoors in a paper bag until the weather became consistently warm by late May. Then, I carefully tied the egg cases to hidden branches of shrubs in my yard. By July I began to see smaller green mantises in the bushes.

As the summer progressed, I observed dozens of swallowtail butterflies in my garden as well as a few monarchs. It was a joyous sight to watch them flutter from flower to flower. I have never had so many butterflies in my yard before and I think the reason for this was that there were fewer Chinese mantises.

I will continue my experiment with praying mantises to see if my observations this past year will repeat next summer. My goal is to find a balance in my yard between native and non-native insects to create a healthier ecosystem.

Judith Canty Graves is an Asheville gardener with a background in photojournalism. Follow @TheObservantGardener on Instagram to see new garden photos daily.

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