Mantises are such large, photogenic insects that I really wanted our daughters to be able to see one. Unfortunately, I’ve never seen one in the wild here in the Upper Peninsula of Michigan (although they are reasonably common in the part of the Lower Peninsula where I grew up). So, we decided to raise some from purchased eggs. We got ours from Arbico Organics [1], who specialize in biological pest control agents. The egg cases were for Chinese Mantids, Tenodera aridifolia. They sent us three egg cases in a plastic tube for, I think, about $10 plus shipping.[2] After incubating them for nearly 6 weeks, this is what we got:

There were well over a hundred baby mantises from each egg case, so we ended up with an embarrassingly large number. They were cute, spindly little fellows, each maybe a centimeter long.

We fed them wingless fruit flies from a culture that we bought from North Country Pets in Laurium. At first we would open the lid and pour in the wingless fruit flies periodically, but after a while we just opened up the fruit fly culture jar and put the whole thing in. The fruit flies were a perfect size for the baby mantises to eat.

There were so many mantises, and they were so tiny, that they were impossible to keep contained perfectly. Every time we opened the cage to feed them a few would get out. So, we had a number of them roaming around the house for quite some time.

Even though mantises are notorious cannibals, they lived together pretty well for the first month or so. Probably because they were all about the same size, and had plenty of fruit flies to eat. They grew well, and once it finally warmed up enough outside we released probably 90% of them out in our garden, where we later spotted them from time to time for a lot of the summer [3].

We experimented with a couple of different kinds of enclosures, but the only thing that seemed to work was the original aquarium with the moistened soil in the bottom, and misting with water every day or so. They just have so much surface area that they are very prone to drying out, at least when they are small.

About the time they were a month old (after the 3rd molt) was when the cannibalism set in, and the population in the aquarium abruptly crashed. It only took a few days, and the trigger was that some of them got bigger than the others.

One in particular managed to get to its fourth molt first, making it substantially bigger than the others for a critical few days. Then it went cruising around vacuuming up its few remaining siblings until none were left. Once it had the size advantage, the rest didn’t have a chance. Here it is molting again after the carnage.

By this time, it was big enough to graduate from fruit flies to bigger prey, so I started going out with the sweep net every few days to collect miscellaneous insects from the tall grass. I’d just sweep a couple of times to collect several dozen assorted insects, sort out any predators that might have been big enough to threaten the mantis (like crab spiders), and then dump the rest in the cage. It was willing to eat most things, but there were a few insects that it consistently snubbed, like stink bugs. It also had a particular prey size preference, it was particularly interested in prey between about 1/4 and 1/8 its size. The mantis then started growing really fast, going through a molt every week or so until it reached its adult size in the middle of August.

It was able to walk upright on the ground, but it greatly preferred hanging from the roof of the cage. I suspect that’s probably how these mantises normally hunt; hanging from the underside of branches and leaves. It certainly wanted to hang upside down to molt, as this allowed it to pretty much just drop out of its old skin.

The wings were amazingly tightly furled when it first came out of the last skin, but they soon unfurled completely.

Once its exoskeleton had hardened, it was ravenous, and would eat an entire grasshopper in just a few minutes. The thing is, mantises have no venom and no real way to quickly kill their prey. So, they just grab their still-living victim and start eating as it squirms, which is pretty gruesome. At least they have the decency to normally start from the head, which probably kills the victim slightly faster than just gnawing on it at random.

Ah, delicious. Happy thanksgiving!

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[1] Arbico’s mantis egg shipping season runs from January to June, so they aren’t available right now as I write this.

[2] This was actually our second try on raising mantis egg cases. The first time, I made a blunder and put them into an open-mesh cage with no moisture source. Indoor air gets pretty dry around here in the winter, and the eggs dried up and died. It turns out that mantis eggs don’t hatch unless the air is at least 40% relative humitidy, and do best at closer to 80% humidity (and a temperature of about 70 degrees F). So this year, we set up a 10 gallon aquarium with a screen lid and about 3 inches of soil in the bottom, thoroughly wetted the soil with almost a half-gallon of water, and then put in a handful of dry straw bedding for the egg cases to rest on. We also put in a thermometer/hygrometer combination so that we could keep track of moisture and temperature, and periodically misted them with a water spray bottle if the humidity dropped to about 75%. This worked great, we had all three egg cases hatch out this year.

[3] Why I Am Not Concerned About Mantises As An Invasive Species: First, I don’t think that this mantis species is capable of getting established as a breeding population here in the first place. They needed six weeks of above-70-F temperatures just to hatch. Given our rather chilly climate, this would put their local hatching date in the wild at sometime around the middle of July. And, it took four months for our fastest-growing individual to make it to maturity, which means that a hypothetical July-hatching mantis wouldn’t be ready to lay eggs any earlier than October. We’ve usually had our first hard frost by then, so the odds of one living long enough in the wild to lay eggs are pretty negligible. And, of course, even if they did get established, the odds are they wouldn’t have any deleterious effects anyway. They’re just one more generalist predator. And if they get above a very minimal population level, they cheerfully eat each other, so their populations are self-limiting anyway. Which is why I don’t feel bad about releasing them into the garden.

[4] I’m pretty sure this one was a male, his abdomen didn’t become as huge as I would expect from the females. He was still alive when I started writing this page, but in the last couple of weeks of September his appetite tapered off, until finally he refused to eat altogether. Finally, on September 28, he died, so it looks like the male Chinese mantises only have a lifespan of about 5 months. If we’d succeeded in raising a female as well, he could have gone out in one last blaze of glory as he mated with her while she ate him, but as it was he just faded away from old age. Which was kind of sad.