COLUMN: Praying Mantids: Alien invaders or beneficial insects?

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By Bryce Roberts

One afternoon last week while I was out walking my dog, I was inspecting some wave petunias and marigolds that my family had planted in a large pot next to our garage.  I was making sure that they had plenty of moisture and that there weren’t any bugs eating on them.  Moisture was fine and didn’t see any bugs so I began to “deadhead” the flowers or pulling off the old blooms.  
When I lifted some of the wave petunias up, that’s when I saw it:  a Praying Mantis.  It was the first praying mantis or mantid that I had seen in a couple of years.  I’m always and have always been curious when it comes to our insect friends, but have been particularly intrigued by the mantids.
One of the characteristics that raises my curiosity about the mantid is the way they look.  They are some of the most distinctive insects because of their elongated bodies and triangular heads, hence the alien invader look.  They also have spiny front legs in which they use to grab their prey.  When they are about to attack another insect, they assume a “praying” position, hence their common name.  Also, they are able to rotate their heads 180 degrees so that they have a good field of vision to look for their prey with their large eyes.
There are three species of mantids in Kentucky:  the European mantid (Mantis religiosa), Carolina mantid (Stagmomantis carolina), and Chinese Mantid (Tenodera aridifolia sinensis).  The Carolina mantid is a native insect to Kentucky, while the other 2 were brought in to the United States about 75 years ago as a natural predator to other insects.
The mantids go through a simple life cycle, which includes egg laying, nymph stage and adult stage.  The nymphs resemble small, wingless adults.  After hatching from eggs in late spring, the predatory nymphs feed and grow through the summer, molting several times before becoming winged, mature adults.  In late summer and early fall, female mantids attach large egg masses to twigs.  These egg masses often contain hundreds of eggs, and are constructed with a gluey substance that quickly hardens, providing protection from birds and other predators.
Mantids are not necessarily considered beneficial insects, even though they will eat other insects, including certain fruit flies and pinhead crickets.  The reason that they are not considered beneficial is because they are cannibalistic, meaning they will eat one another if there is not enough food to go around.  You can buy egg masses and put them in your garden to hatch for the spring, but if there’s not enough food to go around, you’ll be left with just a few mantids.  They can also consume other benficial insects.
So, to answer the question in the title of this article, Praying Mantids are neither an alien invader (not from space anyway) or a particularly beneficial insect.
I hope that my experience with the praying mantis piqued your curiosity as well.  If you want more information on praying mantids, you can go to www.ca.uky.edu and in the search box at the bottom left of the page, just type in “Praying Mantis” and it will bring up some publications from where I received information for this article.  There are also some good pictures there as well.
Feel free to contact me at your Spencer County Cooperative Extension Service at 477-2217 or you can email me at broberts@uky.edu.  You can visit the Spencer County Extension Services’ website at www.spencerextension.com.
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