While you are tidying your yard this spring, please be on the lookout for mantid egg cases (oothecae). There are three introduced species where I live in Pennsylvania (Delaware County): the Chinese mantid (Tenodera sinensis), the narrow-winged mantid (Tenodera angustipennis), and the European mantis (Mantis religiosa). We have only one native species: the Carolina mantid (Stagmomantis carolina). Below are photographs of their oothecae.
Chinese mantid (Tenodera sinensis)
Chinese mantid oothecae are typically round (or roundish) roughly textured, and uniform in color.
Narrow-winged mantid (Tenodera angustipennis)
Narrow-winged mantid oothecae are usually rather elongate (in contrast to Chinese mantid and Carolina mantid oothecae). They are also seem to have red streaks, though the color seems to be most noticeable after they age a few months.
Carolina mantid (Stagmomantis carolina)
Carolina mantids form relatively smooth, teardrop-shaped oothecae with a central portion that is lightly colored. In addition to branches, often found on tree trunks, rocks, and buildings.
Note: Missing from above is a photograph of a European mantis (Mantis religiosa) ootheca, another introduced species that occurs in my area (Delaware County, Pennsylvania). Here’s another pic. They should also be destroyed. Another common name for the European mantis is praying mantis (not preying mantis).
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. 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.
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 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, e.g., 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 passed down for generations, and perpetuated by individuals who support themselves by selling egg cases online. 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 birds). I.e., when a mantid is fully grown it will not even look at an aphid. If you really want an insect that eats pests, go buy some ladybugs or lacewings. 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.