Mantis Musings

It is spring, and any given week from mid-April to late May we may have 200+ students visiting for various outdoor/nature programs.  I love turning them loose to see what they can find, and given the opportunity, they make many amazing discoveries.  

Recently, we had a group participating in our Biodiversity Investigation program, which has them walking through two different habitats (woods and prairie), looking for (and recording) signs of wildlife.  Often, this means insects, although sometimes we find birds, animal tracks, dens and nests as well.  Under the bark of decaying trees, or in the wood of rotting logs, are some of the best places to explore.  The grassland is a little more of a challenge right now, because it hasn't been quite warm enough for the critters to be out and about.  Never the less, our group had a great find:  not one, but TWO praying mantis egg cases.

 Egg case of the Chinese Praying Mantis.

Egg case of the Chinese Praying Mantis.

These are great finds because a) they are so odd-looking, and b) they are not something most people encounter.  We left the first one out in the field, but the second one I brought back in to the office to see if we could get it to hatch indoors and share with visitors.

Thanks to a post that came through on my Facebook feed this week about how we should destroy any eggs cases we find like this, for they are from the non-native Chinese praying mantis, which is apparently some consider an invasive species, I decided to do a little research. 

While there are about 2000 species of mantises/mantids found worldwide, North America is home to about 21.  Of those, only one is found in our neck of the woods:  the Carolina Mantis (Stagmomantus carolina).  Two non-native species are found here, too, and in much greater numbers:  the Chinese Mantis (Tenodera aridfolia sinensis) and the European Mantis (Mantis religiosa).  Both have been here over 100 years and are considered "naturalized."  

Last summer we had a beautiful enormous specimen clinging to the porch screen for a couple days right outside our entry way.  Simply because I knew that the Chinese mantis was quite common, I presumed that was who she was (pretty sure it was a female, too, because her abdomen was very large), but yesterday I started wondering:  would I know our native mantis if I saw one?

As it turns out, telling our native mantis from the interlopers is pretty easy, primarily because it is so small by comparison.  S. carolina is about two inches long (compared to the whopping four to six inches of the Chinese; the European falls in between, but on the larger side).  Its wings only cover about 2/3 of its abdomen (100% coverage for the other two), and its colors are mottled, either in browns or greens (the others are more solidly brown or green).  Our native mantis exhibits no spots between its two predatory front legs; the Chinese has a yellow spot, while the European sports black or black and white bullseye spots.

 Found this good ID/comparison photo online - thanks to John Meyer of NC State University.

Found this good ID/comparison photo online - thanks to John Meyer of NC State University.

If you find a hard, frothy-looking egg case (ootheca), you can tell if it is native or not by the size and shape.  Our native mantids' egg cases are small, and are longer than they are wide.  The Chinese mantis egg case is fairly stout, almost round - as seen in photo above.  The European mantis egg case falls in between - longer than wide, but not as narrow as the native ootheca.

 Native Carolina praying mantis egg case - thanks to S. Carolina Public Radio.

Native Carolina praying mantis egg case - thanks to S. Carolina Public Radio.

So this brings us to a conundrum:  are the non-native mantids good or bad?  It depends on who you talk to.  Gardeners love them, because they are providing a beneficial service by eating many insect pests.  However, the fact that our native species is becoming so difficult to find suggests that perhaps they are being elbowed out of the picture by the non-native species. 

Additionally, the Chinese mantis is known to voraciously eat whatever it can catch, including butterflies, beneficial pollinators, tree frogs and even hummingbirds!  Is it also eating our native mantids?  Sounds to me like that is quite possible.

The debate is raging on the Facebook post (it came through my feed again last night), so I sent an email to APHIS to get the official status.  (I've been waiting two weeks for an answer...none received to date.)

So we are left with a quandry:  do we keep the egg case we found on display for visitors, or do we destroy it?  It's a difficult choice to make.