Sunday, February 24, 2008

Carolina Mantis Migrating North?

I happened by a construction site on the eastern shore of Virginia last week. The site has been a fallow cropfield for several years. Figured I would save a few native seeds (or plants) and call it my good deed for the day. What I found was much more interesting.
This eggcase (ootheca) morphology was just similar enough to the ever-popular Chinese Mantis (Tenodera aridifolia sinensis) that maybe - just maybe - I had found a colony of mantids from an entirely different species. Once I had collected about 30 oothecae (remember, this site will be under pavement in about 90 days), I was suddenly stricken by fear at the outside chance that I was helping to spread some other critter whose eggcase I don't, say, the desert locust! Since this field is between a highway and a railway, it could be anything! Gulp! So I ran home and looked for some answers on the website that our president refers to as, "The Google."

Answer found!

Since most of my fieldwork south of the VA/NC border has been in the mountains, I was not really familiar with the Carolina Mantis (Stagmomantis carolina), an inhabitant of warm season grass fields, emergent wetlands, and tall pastures throughout the southeastern piedmont and coastal plain. I continued my "internet research" (gotta love kids these days!) and while most of the internet references to S. carolina are from natural history museums and state agencies from North Carolina to Florida, and just a few from Virginia and states north. Apart from the beloved,; most of the "northern" descriptions make a note of observations that the local populations of S. carolina were historically unknown or uncommon, but now seem to be increasing.
Now, I know that it's a mighty big inferential jump to assume that since these very anecdotal descriptions of "increasing populations" on the fringe of S. carolina's range might actually represent species migration.........but humor me for a moment.

Here in the mid-Atlantic, we have not had a "significant" winter for 5 or 6 years. Since mantids die after fall mating, adult over-wintering is not a limiting direct factor for the species. However, I do know that extreme cold temperatures have a major effect on the viability of insect eggs. Since most of my career has been focused on species that are NOT increasing in number or range, I simply don't have a good theoretical background on what may be happening with the Carolina Mantis. Is it possible that mild winter temperatures in the existing range (increased hatch success), combined with mild fall temperatures on the northern edge of the existing species range (increased adult growth, mating & egg-laying success) are combining to move this species northward into a new range?

And the $200 questions: Will its movement north be impeded by the larger Chinese Mantis? What will its effects be on highly valued pollinators, as well as the few remaining native mantids in the Great Plains and north central states? Or, if we have two solid winter seasons in a row, do all the Carolina Mantids vacate the upper Mississippi, prior to ever reaching the Great Lakes?

Did anyone notice that I didn't mention global warming one time?


pinenut said...

What a fascinating observation. Maybe you could add this post to a blog carnival that attracts insect specialists to see what they think--maybe Circus of the Spineless.

Is there a blog carnival devoted to global warming? I wonder what it would be called. . . .

Tom said...

Swamp Thing-

Interesting Stuff. You have presented here a very logical argument with several important questions. This sounds like a dissertation project to me!

It could involve some field work, some laboratory experiments looking at survival temperatures of egg masses, and even some mesocosm studies where you could rear both the Carolina mantis and the Chinese mantis to see if one out competes the other and for which resources.

In Ohio we have many southern plant species that will gradually increase there range northwards until one harsh winter, like that of 1978, where all the individuals are wiped out and the clock starts over again.

Happy blogging,

Tom @ Ohio Nature

Swamp Thing said...

Pines - there are a couple of bug blogs. It's worth venturing over there....let's see if I can solicit some posts.

Tom - the status of this "migration" after 1 or 2 harsh winters really would tell us a lot. We experience the same thing here with chickadees, flying squirrels, and several coastal plants.

Walter said...

Hi! I did not read your stuff so sorry. I just want to say that Chinese Mantids are now a species, Tenodera sinensis Saussure, 1871 and they used to be a subspecies in the species Tenodera aridifolia which has three subspecies, Tenodera aridifolia aridifolia, Tenodera aridifolia angustipennis, Tenodera aridifolia brevicollis and Tenodera sinensis used to be a subspecies of Tenodera aridifolia, Tenodera aridifolia mandarinae before it was Tenodera aridifolia sinensis. All of those oothecae in the picture are Tenodera aridifolia angustipennis oothecae. I got this information from Bye. I will read it.

River Mud said...

It's a bold statement to make that those cases are not Carolina mantids. From your location, I can tell that T. angustipennis are common in your area, and Carolinas do not exist.

Everything I've read has said that perhaps 100 people in the world could differentiate the two egg cases in the field. And since that site is approximately 200 miles from the "Carolina" in Carolina Mantis, and 12,000 miles from China, I'll go with Carolina Mantis as my safe bet.