March 18, 2016
Chinese Mantids
Everyone knows that you shouldn’t put all your eggs in one basket. But what I need to remember is to also not put them all in one tennis ball canister, nor leave them all on one desk.
Or any desk, actually.
Our current situation got its start about a month ago, when Roger Hotham, long-time volunteer at Bluff Spring Fen in Elgin, brought us a gift of a dozen or so oothecae—the fancy name for egg cases—from two different species of praying mantis: the Chinese, Tenodera sinensis, and the European, Mantis religiosa.
Roger and I have a shared interest in the effect these two introduced species are having on populations of native arthropod predators—namely spiders—in local grassland areas. He noticed several years ago that as Chinese mantis populations increased, the numbers of spiders—particularly the conspicuous black and yellow Argiopes (a.k.a. banana spiders or garden spiders)—were decreasing.
When we last spoke, he said he wished he had empirical data to back up what seems to be happening. But even without it, his anecdotal evidence is pretty compelling.
At Bluff Spring Fen, he works with a number of other dedicated folks that come out to help with various tasks, including seed harvests. While harvests can be held at various points throughout the year, depending on habitat, most prairie species set their seeds in late summer and early fall—the same time Argiope spiders are most evident.
Now, among Roger’s volunteers was a woman who was very enthusiastic about all the restoration efforts at Bluff Spring Fen, including seed harvests. But when it came time to collect the prairie seeds, she had to excuse herself—for a very powerful reason: She had extreme arachnophobia. Gathering seeds in a natural area rife with spiders was akin to walking through fire, as far as she was concerned.
However, Roger noticed, with the rise in mantis numbers and the corresponding drop in spiders, his loyal volunteer was able to participate in fall harvests fear free. The shift in invertebrate fauna was great for her, and good for Roger and the site’s seed harvest goals. But could it ultimately be bad for the diversity at the fen?
We don’t have an answer to that yet. But what we do have, thanks to Roger’s commitment and keen eyes, is a whole bunch of praying mantis egg cases. Interestingly, over the past few years, the Chinese mantids have been joined by members of the European species. Various differences exist between the two insects – size at maturity, and markings, to name a couple.
Likewise their egg cases sport differences too. Those of the Chinese species are about the size and shape of a lightly toasted marshmallow—yellowish brown and squarish. The European species’s ootheca, by contrast, is more oblong in shape.
I’ve actually gotten quite familiar with both of them, as they’ve been sitting now for over a month in the aforementioned tennis ball canister atop the aforementioned desk—which happens to be mine.
At first I wasn’t overly concerned about this arrangement. After all, two years ago when Lisa O’Brien, our school program coordinator, and I collected over a dozen Chinese mantis egg cases in hopes of getting a baby mantis to raise, we had zero success. The cold temperatures that winter may have had something to do with that poor hatch rate; the shock the eggs underwent when they were introduced to warm indoor temperatures might also have played a role.
But this year… Well, let’s just say that this year is a different story.
I noticed the first baby mantids a few weeks ago. I was in the middle of a fairly intense phone conversation when I happened to look over at a file folder I had lying open. There, crawling across– in a twist of irony, some endangered species paperwork–was a tiny Chinese mantis. I looked over toward the pile of ootheca and, sure enough, the egg case on top was literally crawling with babies.
Two hundred? Three hundred? I wasn’t even sure how to begin counting.
I was also at that point pretty unprepared to deal with the deluge. Luckily for me, though not the mantids, the dry office air took its toll. Most did not survive the emergence.
Given our poor hatch rate from 2014, it wasn’t hard to tell myself that that first case that had opened would be the one and only. Nonetheless, from that point on, the egg cases resided inside a tennis ball canister.
And good thing! As the weeks have progressed, so have the mantid eggs. Several more of the Chinese cases have opened up. Last week I took the lid off the tennis ball can and transferred the whole roiling lot to a large plastic pretzel barrel. This week I subdivided the group into assorted gallon-size pickle jars.
Today, inside their now-spacious living quarters, they’re thriving. They’re currently benefitting from plentiful food—in the jars, as in nature, the stronger prey on the weaker—as well as water in the form of droplets of mist added every other day. The plan is to let them duke it out a while longer, until a few dominant individuals emerge, then separate them into separate living quarters where they can continue to grow, feasting on assorted insect prey, the size of which will increase as the mantids themselves get larger.
With any luck, we’ll be able to get a few of the European species to grow too, and we’ll end up with a nifty praying mantis display here at Hickory Knolls. I’m not sure yet how we’ll house them yet—probably in an assortment of enclosures we can set up on the front desk.
Large glass jars? Possibly. Small glass tanks? Maybe. One thing’s for sure—they definitely will not wind up all in one basket.
Pam Otto is the manager of nature programs and interpretive services at the Hickory Knolls Discovery Center, a facility of the St. Charles Park District. She can be reached at 630-513-4346 or potto@stcparks.org.
Sometimes considered cute, and charming, Chinese mantids also are predators that may be putting pressure on populations of native arthropods, including Argiope spiders.