Below are photographs and descriptions of egg cases of the (native) Carolina mantis, the European (=praying) mantis, the Chinese mantis, and the narrow-winged mantis.
Carolina mantis 
European mantis 
Chinese mantis 
Narrow-winged mantis
Carolina mantid (Stagmomantis carolina)
Carolina mantids (the only native species in my area) form relatively smooth, teardrop-shaped oothecae with a central portion that is lightly colored. Often found on tree trunks, rocks, and buildings.
European mantis (Mantis religiosa)
These oothecae are somewhat similar to the Carolina mantis’ but lack the alternating bands of color. Another common name for the European mantis is the praying mantis.
Chinese mantid (Tenodera sinensis)
Chinese mantid oothecae are typically roundish, roughly textured, and uniform in color. Introduced from Asia, as you probably guessed.
Narrow-winged mantid (Tenodera angustipennis)
Narrow-winged mantid oothecae are usually rather elongate. They are also seem to have red streaks, though the color seems to be most noticeable after they age a few months. Introduced from Asia, too.
More ID help
For an excellent overview of all of these species, please see the Cape May Wildlife Guide’s page on mantids. If you need help identifying an ootheca, I highly recommend posting a photograph on iNaturalist. Not only will you get an answer from the iNaturalist community within a day or two, your submission helps scientists track the spread of invasive species.
What should you do with the non-native oothecae?
Invasive mantids eat butterflies, native bees, honey bees, small birds, and also the native mantid, so when you find egg cases, dispose of them. Here are some suggestions on how to do that:
- Give them to local bird rehabilitation centers — if local bird rehabilitation center doesn’t know what you’re talking about, inform them that insectivorous birds absolutely adore frozen mantid hatchlings.
- Give them to a neighbor who has chickens.
- Give them to a neighbor who has a pet tarantula, snake, lizard, or fish.
- Put them in a freezer for a week.
- Step on them.
Whatever you do, please not just relocate oothecae to some nearby field — that just transfers the problem to someplace where you can’t see the problem.
But aren’t mantids great for pest control?
This is a myth. Although it’s true that young mantids consume a lot of insects, some of which might be pests, when mantids are fully grown they tend to camp out on flowers and wait for large butterflies and even small birds. Mantids are, of course, excellent for controlling butterflies and hummingbirds in case you happen to hate those animals.
I saw about 20 Chinese mantis egg cases at Hildacy preserve a few months ago :/
There’s a small tree at Hildacy with 12 egg cases. I wish Natlands would hold egg-case hunts on Easter. Would be great fun, and kids would really enjoy, too.
Curious to learn how you came up with your opinion?
Feel like this is just a high school essay, with no actual realistic facts…
My primary source is just my yard. Started noticing piles of monarch wings underneath certain plants, then realized it was likely the Chinese mantids camped out there. After a little research online, turns out that these mantids have a known ability to selectively eat the parts of monarchs and thus avoid the bulk of their toxicity.
Chinese mantises were introduced more than one hundred years ago, and have successfully integrated into our ecosystem–there’s no need to go destroying these magnificent insects. “Invasives,” whether plant or animal, are often subjected to xenophobic persecution for no valid reason. Nazi Germany was the first nation to legislate their exclusion. It is true that they can disrupt an ecosystem, but generally over time the problems they create will dissipate as the dynamics adjust. David Theodoropoulos’ out of print “Invasion Biology–Critique of a Pseudoscience” furnishes an excellent analysis, and addresses the hysteria to which we’ve all been subjected regarding this issue. Get a copy if you can find it!
I hadn’t heard that Hitler hated Chinese mantids. Thanks for the reading rec. I’ll check it out.
Exactly. This guy is dangerous with the words he’s putting out.
I probably wouldn’t kill a Mantis sac if I had found one..but I’m glad that I did find a few Carolina mantis egg sacs on the shed here in Philadelphia today.
That’s fantastic!
No what’s fantastic is that a few weeks ago I actually picked this female mantis up off the sidewalk and put her in the grass. A few days later she was on my shed and has moved but hasn’t left. And I caught her eating a spotted lantern fly the other day… now she’s laid a sac or two
Promotion of smashing egg sacs of the mantids is sick and twisted. Completely uncalled for. They’ve been here since 1896 at least. You should be ashamed of yourself.