How harmful are introduced mantids in the US?

I live in Indiana, where we have one native mantis species, the Carolina mantis, and three introduced mantids: the Chinese mantis, the European mantis, and the Narrow-winged mantis. The Chinese mantis, in particular, is very common here, and it’s 50% larger than the Carolina mantis.

I found and caught a Chinese mantis on a bush this week, and several of my friends encouraged me to let it go. I was reluctant to do so, since it’s a non-native species, and I ended up giving it to one of those friends to keep as a pet. But I realized I don’t really have any idea whether our introduced mantids are actually harmful for the native mantis populations, or for the prey insect community in the area. Since they are big, I can imagine Chinese mantises might outcompete our Carolina mantises, but since neither species is that abundant, I can also imagine that they might interact very little.

What do you think? Does anyone know whether our introduced mantids are harmful “invasive” insects or benign “naturalized” species?

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From what I understand, there’s not strong evidence either way (awful invasive vs. neutral naturalized), but some evidence that invasive mantids do have ecological impacts at least. There’s anecdotal evidence that they may outcompete native mantids in the US. A longer form look here:
https://www.insidescience.org/news/lessons-about-love-and-invasion-americas-foreign-mantises

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I am not fond of the huge Chinese Mantis because there are documented cases of them catching and killing hummingbirds.

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I feed them to my chickens.

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I have also observed Chinese mantids eating monarch butterflies. And I’ve found husks of caterpillars, too, underneath where I found a Chinese mantid. Anyone who wants to encourage pollinators might want to patrol for invasive mantids in their yard.

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I observed a Chinese mantid eating a monarch caterpillar and leaving the husk also.

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Yeah. They don’t distinguish between native pollinators and pests when they feed.
https://www.inaturalist.org/observations/17082492

I have a feeling (obviously unproven) that they have a role in the decline of bees…workers leave the hive and don’t come back
https://www.epa.gov/pollinator-protection/colony-collapse-disorder

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I was hiking through Soldier’s Delight Natural area and saw a lot of the Chinese mantids in the meadow. The Liatris were in bloom, which attracted the big butterflies. I repeatedly saw the big mantids eating the butterflies. I took pictures. Thanks for posting, you’ve inspired me to go get them and post them on iNat. Later in the late summer/fall I found one in the native asters in my front yard, she was eating a bumblebee. It felt unfair to plant natives in my yard to attract pollinators and then let them be eaten by an invasive predator - so the predator was dispatched :-(

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I have a monarch waystation and a lot of Chinese mantids in my yard, and yes they do a number on those butterflies and caterpillars. When I catch an adult in my milkweed patch, I will move it to where it can be more beneficial, e.g. to my blueberry shrubs to clean up the yellow-necked caterpillars on those. I don’t like killing them outright so I try to put them to use in other places or give them away to families with children to keep as pets. I have on occasion destroyed egg cases over the winter if I find more than a dozen around the yard. Up to a dozen I like to move to my greenhouse for pest control in spring. The little ones are great at catching aphids. And since my greenhouse is full of Venus flytraps at that time, a lot of them eventually become plant food, haha. Those who escape the horror and made it out into the yard have earned their freedom at least.

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I should review more about these if I wanted to give a fuller answer. But from what I know, these species are abundant and were introduced somewhat long ago (correct this if wrong). As far as harm, I at least think they can all even cannibalize their own species, including I’ve seen one offspring eat another.

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I would imagine that even if it hasn’t been rigorously studied, they do a sizeable amount of damage considering how abundant they are (both in terms of range and population size) and how much larger they are than our native Mantis species-- they wouldn’t be eating the same things that natives would, and it’s harder for native predators to utilize the Asiatic species as a new food source because of their size and combat abilities. As someone said, they’ve been seen killing hummingbirds, so they’re probably somewhat of a threat to insect-eating birds that would try to predate them (so there are probably very few birds that would bother trying to eat them).

Additionally, in regard to dealing with them… I have always heard that freezing insects is a humane way to kill them, although there is some debate over that since it’s not an immediate death. If you can’t bring yourself to carefully squish the foreign mantises in a single, swift try, then that would probably be a good option to get rid of them.

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My experience is different. Fortunately they’re still relatively uncommon in my area. I probably find 1 or 2 per year compared to the dozens of Stagmomantis I come across almost every month. I would say they’re naturalized for now.

In terms of are mantises harmful or pests, they aren’t a societal pest. They’ve been valued since ancient times, e.g. for preying on insect pests in gardens. This source which calls itself a conservancy does suggest the two exotic species are invasive and could outcompete or prey on the native species. But, it also mentions they can spread through pet stores and people use them for gardens.

The fact that stores sell them probably means their harm hasn’t been significant enough yet to result in stronger regulations against their sale/use. The largest possible harm may be to the native mantis species or possible some other insects, but I don’t know how significant that is. I doubt hummingbirds are significantly harmed by them, I assume those attacks or successful predation events are fairly uncommon.

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Chinese mantises have been in the U.S. for over 100 years and, due to their place in the middle of the food chain, their ecological effect is neither “good” nor “bad” but complex (e.g. Snyder and Evans 2006). At this point, I don’t think there is much point in killing individual Chinese mantises simply because they are non-native. Whether we like it or not, they are now an established part of American ecosystems, just like house sparrows and eucalyptus trees. Luckily, the native Carolina mantis (which some consider to be two species) seems to be holding its own and doesn’t seem to have been displaced by the Chinese mantis (although its population levels are surely lower due to competition). As far as bee and butterfly predation, the only real threat to bees and butterflies is humans, not mantises. Poorly regulated pesticide use in industrial agriculture is decimating insect populations in North America and elsewhere. Instead of killing mantises we should be championing organic food and lobbying for better pesticide regulation, at least in my opinion.

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I seriously doubt colony collapse disorder has anything to do with mantids
when we’re cramming several hives in one area and facilitating the spread of disease, as we tend to with livestock in the modern era, and also wildly overusing pesticides, I’d think that might be the root of the issue

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Ahhh thats interesting. For me its usually the opposite, tons of Tenodera when mantis season comes around, and only a few Stagmomantis. I wonder what environmental factors are driving that

I agree.

I agree.

Technically some additional insects (including some bee and wasp species) or other wildlife predators can be a threat, such as Asian Giant Hornets for honeybees. Having said that, it depends on what we define as a threat. Few things would threaten the extinction of a species. Mantises are predators which can also eat bees and butterflies, although I haven’t heard that they particularly result in many losses (compared to predatory wasps, etc).

Interestingly enough, native Stagmomantis species (mainly S. limbata, the arizona mantis) also prey on hummingbirds regularly despite their significantly smaller size. In fact, I think I’ve seen more photos of arizona mantids eating hummingbirds than chinese mantids.

Mantids eating hummingbirds is still a somewhat unnatural occurence in the northeastern US where chinese mantids are established though, since carolina mantids seem to generally be too small to catch hummingbirds (though there’s a few pics/videos of them trying).

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Dragonhunters do definitely take hummingbirds on occasion, though, so not entirely unnatural for insects to be rarely predating on them up here

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Is the understanding basically just that mantises attack/attempt to prey on all organisms of insect size or larger? (with possible exception of and if there are any insects with coloration indicating toxicity). In other words, they aren’t exactly attacking birds because they’re birds, just attacking everything. I can’t remember, I’d guess they also attack some small mice, frogs, etc. occasionally?

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