Last month I wrote about lady beetles, also called ladybugs, and discussed some of the problems with buying them as biocontrols for your garden pests. Now, it is the turn of another beloved insect, the praying mantid or praying mantis. Guess what? Just as there are many species of lady beetles, there are also many different mantises. The good news is that while lady beetle species number in the hundreds, there are only twenty kinds of mantises.* The bad news is that four or five of those species are not-native and may be causing problems for the native ones.
Mantises are charismatic insects because of their remarkable looks and because they are considered a gardeners friend, eating numerous bugs. Some value them as pets or use them in school projects. The females have the bad reputation of devouring their mates heads, although this is probably largely exaggerated and not as common in the wild as it is with caged ones. They invented Styrofoam long before humans did, more on this below.
Probably, the only one that deserves the name of praying mantis is the European species, Mantis religiosa. However, often we refer to all of them by that name because of the way they hold their front legs as if in prayer, although they hold this posture for more nefarious reasons.
The colors green and brown predominate in most species; colors that serve them well to hide in the foliage. They are not active hunters; instead, they lay in wait for any walking or flying protein passing by, ready to snatch it with those peculiar front legs. The smallest ones are slightly larger than a quarter inch. The larger ones can reach 4.5 in. The females are larger than the males.
Females lay a large number of eggs enclosed in an egg case made from a frothy substance secreted along with the eggs. This soon solidifies into a firm spongy material, natures version of Styrofoam. The newborns are slightly bigger than an eyelash. So dont make the same mistake a friend of mine did, bringing an egg case home and forgetting about it until she found a crowd of little hatchlings scattered on her desk and climbing bookcases. Mantises are notorious cannibals, if the newborns dont find food soon they start eating each other. So, it shouldnt surprise us that females also eat their own kind.
Native mantises are diminishing in numbers probably because of the invasion by those four or five introduced species. The non-native mantises are larger than most native ones. They either out-compete or eat the ones who were here for millennia before the arrival of the newcomers. You are more likely to see one of these introduced species than one of the natives. I keep searching for native mantises, but have only found an egg case of a Carolina mantis (Stagmomantis carolina).
I have already mentioned one of the most common non-natives, the European praying mantis as big as 3.5 in. It has become rather abundant throughout North America, in large part helped by humans selling it to gardens and pet stores. Connecticut has adopted it as its state insect, despite the fact that it is not native. This shouldnt surprise us, though; seventeen states have chosen the equally non-native honey bee as their state insect.
The Chinese mantis, Tenodera sinensis, also introduced, is becoming even more common and widespread in large part due to sales. Pet stores usually sell juveniles, called nymphs, or adults, while garden supply stores are likely to provide egg cases during the winter, to be released in the spring. At 4.5 in, it is the largest species in North America, large enough to trap and eat hummingbirds. This is the one that has become iconic and the one most people have in mind when these insects are mentioned.
Now, for the bad news: I already mentioned that these introduced species of mantis have an impact on populations of native species of mantis. They are also not as good for gardens as we are led to believe. I started checking biocontrol distributors. They sell egg cases of Chinese mantis, giving glowing reports on its function as an insect eater. Prices range around two dollars. This makes me laugh. Where I live, I can find countless egg cases in my winter walks. A meadow with goldenrod patches, multiflora roses or brambles allows me to collect dozens in a couple of hours. Why spend money on something you can pick up for free? If you find none nearby, it means that it has not invaded your area. Then, why introduce this invader? Dont we have enough already? Guess what I do with the ones I find: I bury them. I dont want more Chinese mantises around.
The University of Wisconsin gives this advice: Purchasing lady beetles and praying mantids for release in the home garden is not recommended. North Carolina State Universitys factsheet states: Chinese mantids have no demonstrated value in pest management. They give the following reasons: The insects present in most gardens are not abundant enough to satisfy their needs, so they may eat each other or leave the area. They are indiscriminate in their choices and eat a number of beneficial species, as well as pests. Remember that they can even eat hummingbirds, not to mention other praying mantises, bees, etc.
We have learned much from the beginnings of the use of biocontrols. It is important to determine the target pest, first and then choose a specialized predator or parasite that doesnt disrupt the lives of other members of the biological community. The idea of bringing a generalist predator such as a mantis to your garden has turned out to be a bad idea and it is not recommended anymore.
What can we do in our gardens, then? Maintain a habitat that welcomes and sustains the pest enemies as I mentioned in A Healthy Garden is a Buggy Garden. A few more suggestions are scattered through the pages of this blog. If you think that you absolutely need to use pest controls, dont rely solely on the recommendations of distributors; consult university websites that may provide you with more trustworthy information.
* These numbers refer to species in North America. See: American Insects: A Handbook of the Insects of America North of Mexico By Ross H. Arnett (p.190).
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