There is one native and three introduced mantid species where I live in Pennsylvania (Delaware County), and I’m trying to get the word out that the invasive ones should be killed when found. This post has photographs of the oothecae along with some brief comments about what makes each species distinctive. At the end of the post I have suggestions on how to put the invasive oothecae to good use.
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.
Chinese mantid (Tenodera sinensis)
Chinese mantid oothecae are typically round (or 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.
European mantis (Mantis religiosa)
I’ve never encountered a European mantis ootheca, so here’s a photograph by Hans Hillewaert (via Wikipedia):
Another common name for the European mantis is praying mantis (not preying mantis).
More ID help
If you need help identifying an ootheca, I highly recommend posting a photograph on iNaturalist. If you post there, feel free to include my iNaturalist username (@colinpurrington) in your caption so that I can have a look. 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.
For an excellent overview of all of these species, please see the Cape May Wildlife Guide’s page on mantids.
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.
But whatever you do, do not just relocate oothecae to some nearby field — that just transfers the problem to someplace where you can’t see the problem. I.e., even though you might pride yourself as being a gentle soul that wouldn’t kill a fly, releasing invasive predators will result in monarch butterflies being eaten alive. Don’t be that person. If you simply cannot bring yourself to kill the eggs, ask somebody to help you do the right thing.
But aren’t mantids great for pest control?
Many people (I include myself) grew up being told by highly-educated, seemingly trustworthy adults that mantids are ideal for providing chemical-free pest control in the garden. That view, it turns out, is a myth. Although it’s true that young mantids consume small, pestiferous insects, when mantids are fully grown they tend to camp out on flowers and wait for large butterflies (and even birds). I.e., when a mantid is fully grown it will not even look at an aphid. Mantids are, of course, excellent for controlling butterflies and hummingbirds, just in case you happen to hate those animals.
Some people even believe that mantids can control ticks. They don’t. They are equally ineffective at controlling mosquitoes.