Chinese Mantid Predation on Butterflies

A few weeks ago I wrote this post about the monarch population in my backyard - monarchs in decline isn’t really news though…

It wasn’t until I was clearing out overgrown fennel in our garden this week that I discovered the real culprit…non-native mantises!

https://www.inaturalist.org/observations/57851894
https://www.inaturalist.org/observations/57851889
https://www.inaturalist.org/observations/57851888

After cutting down stalks of fennel I found piles of both black swallowtail and monarch wings in the soil beneath the fennel.

This is the first summer this has happened…usually we have at least 20+ monarch chrysalises and dozens and dozens of swallowtail cats…all of whom eclose and go off into the world effortlessly.

In the future, should I destroy non-native mantid casings when I find them? Usually we enjoy watching them hatch, etc. but not if they are perching at the top of my fennel and grabbing every female butterfly who stops by to deposit her eggs!

Also…I made the horrible discovery of two spotted lanternflies (also non-native and pretty destructive - my county is in a ‘quarantine zone’)…so, would keeping the mantises possibly benefit me in a battle against lanternflies?!?

Also…discovered these informative links to back-up my mantid predation theory regarding the butterflies…

https://ask.extension.org/questions/276876
https://www.nationalgeographic.com/science/phenomena/2013/01/25/chinese-mantis-guts-its-toxic-caterpillar-prey/

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The scattered wings definitely sound like the work of mantids, but I’ve not heard of mantids eating chrysalises, that’s usually done by wasps. Wasps will also cut up and carry off caterpillars, too. It’s very common for me to see paper wasps prowling about on my milkweeds and other host plants in the search for caterpillars. Aside from that, I don’t have much more to offer as Tenodera is still somewhat of a rare sight in my experience. Being outnumbered 20+:1 by Stagmomantis.

Oh! I wasn’t assuming they consume chrysalises, I assumed they consume female butterflies prior to egg-laying. I’ve seen no eggs, no caterpillars and no chrysalises.

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I caught one in the act: https://colinpurrington.com/2018/08/chinese-mantids-eat-monarch-butterflies/. I now kill every Chinese mantid I can find. If you have hundreds of oothecae, donate them to a local bird shelter.

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That is a really, really interesting ecological thought. Weren’t such mantids were sold widely by nurseries as a biological control for garden pests? Such was seen as environmentally friendly compared to pesticides; but, maybe, it really is not as benign as all that?

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They do not do squat for pest control. They mostly eat pollinators. I saw this observation the other day and I think that it perfectly captures the issue that @catttailsandcobwebs raises. https://www.inaturalist.org/observations/57502211 There are a number of good articles out there about the issue. I agree with @colinpurrington’s approach of eliminating them when you can, especially the ootheca (egg cases)

http://mdinvasives.org/iotm/june-2019/
https://colinpurrington.com/2019/03/identifying-mantid-egg-cases-pennsylvania/

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Welcome to the Forum!

Well… so we really were lead down the garden path re: pest control. Many years ago, I got some for my garden and they did seem to eat a lot of aphids. But, I’d no idea what other impacts they could have.

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Mantids will eat spotted lanternflies, but whether it’s enough to matter… :man_shrugging:

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Thank you for the welcome!

The problem I see is that I see them not in gardens all of the time. There is a beautiful place near me, that I frequent, that is loaded with both Chinese and Narrow-winged mantids. They hang out on the goldenrods, the milkweeds, the leafy elephant foot, etc. and there are piles of wings (not just butterflies) below them. The fact that mantids are marketed as a solution to gardening pest control is what really irks me.

I have no idea how large their actual negative impact is on pollinators. I may just be over-reacting. Now about all those non-native plants that have overrun so many places … :smiling_imp:

I actually think that the mantids themselves (even the non-natives :grinning: ) are quite beautiful and amazing, their spread into our natural areas is anything but.

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I used to think that in my area, chinese mantids must be too uncommon to really have a negative impact, as I encountered them very infrequently and they mostly seem to inhabit human-disturbed habitats such as gardens and hayfields and not the forests that predominate. But those sorts of habitats are extremely important for many native insects despite being artificial, and this year there’s apparently been a population explosion as I’ve been seeing chinese mantids in many places and one night just a few days ago I counted at least 36 mantids in a single relatively small patch of weeds along the side of the road. They seemed to have cleaned out all the grasshoppers and katydids that are normally there too.

it sucks because chinese mantids are one of the most beautiful and impressive insects you can find around here, and Massachusetts doesn’t have any native mantids. I usually deal with finding invasive mantids by catching them and keeping them as pets but currently I’m seeing them everywhere and it’s hard to ignore how destructive they must be.

Just for clarification, chinese mantids were not introduced to the US intentionally for pest control- they were accidentally imported with plants over a hundred years ago. I’m sure their distribution has been further spread around by intentional releases somewhat, but they seem to do a good job of dispersing themselves.

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Chinese mantids do perform a beneficial service to cultivated gardens in their early life stages, when they feed primarily upon aphids on plant stalks lower down the foliage. Fully grown adults however have very little benefit to the garden (except for the interest they provide to watch) as they sit high on vegetation and eat primarily bees and butterflies, though if you live where cabbage whites are a pest they readily consume these in large numbers and can be helpful in the garden if you are growing cabbage family crops to prevent infestation.

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It’s undeniable that Chinese mantids will happily eat monarchs, bumble bees, and other pollinators…they’ll eat anything they can grab and subdue, including hummingbirds. I can’t argue against trying to control them, though personally I’d find it hard to destroy such a big, charismatic insect. (Egg cases, though–that’s another thing. No problem there.)

However, given that the Chinese mantis has been in North America since 1896, it seems unlikely that it alone is to blame for the recent decline in monarchs. Other factors, primarily deforestation in overwintering sites, increased monoculture and “weed” control that has wiped out much of the milkweed they require, light pollution, and the proliferation of automobiles are likely much bigger factors.

All in all, though, this has been a pretty persuasive discussion that Chinese mantids may do more harm than good. It would be nice to see our native mantids more frequently than these big predators…the Siberian tigers of the insect world.

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Yea, I certainly would have difficulty destroying an adult…egg cases, no problem.

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Lep guy here who rears a lot of caterpillars. Not really an expert on mantises, but it seems doubtful to me that they would actually have a noticeable impact on any of their prey species’ population. I feel like mantises come in relatively low densities compared to other predators and are fairly generalized in their feeding habits. I would imagine the odds would be low that a given mantis would attack the same prey species enough times over the course of its life to have an impact on the population.

On the other hand, to put things in perspective, parasitic wasps and flies (both native and introduced as pest control), which often specialize on a single order or family of insects, have most definitely single-handedly caused the decline of a number of Lepidoptera species. I wouldn’t be surprised if parasitism mortality was as high as 50% in some populations. If you’ve ever gone collecting caterpillars to rear like I do, you’ll sometimes end up with more wasps/flies than butterflies/moths. I know for sure that tachinids are quite a big problem with monarchs and I’ve also had problems with Trogus pennator in wild collected swallowtails.

Other predators that I would imagine that probably have a much larger impact than mantises are paper wasps and stink bugs. I use mesh sleeves when rearing caterpillars outside to protect them and these are the most common predators I see trying to break in. I once intentionally removed the sleeve off a clutch of a hundred or so swallowtail larvae to see if they could survive on their own, and over the course of several hours I witnessed virtually all of them be abducted by paper wasps. With the stinkbugs, even with the sleeve over the caterpillars I often catch multiple of them on the same sleeve piercing the caterpillars through the mesh. They’ll go for the eggs too - I’ve seen plants with several dozens of unhatched eggs completely sucked clean by stink bugs. Needless the say, I’m actually quite surprised you regularly have dozens of monarchs and swallowtail caterpillars survive without protection. Assuming that the survival rate of the species probably hovers around less than 5% (otherwise there’d be exponential growth), that’s probably an anomaly rather than the norm. Anyways, I should problem stop here before I go off on a tangent on more caterpillar rearing (unless you find it helpful of course)…

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Well, the difference is that Trogus pennator is a native species that’s supposed to prey on north american swallowtails. I’ve also raised swallowtails and had many of the larvae turn out to be infected by Trogus, but enough survive that I still find plenty of caterpillars each year.

of course, invasive parasitoids certainly are a problem, and there’s good reason to think that the intentionally introduced Compsilura concinnata is responsible for extirpating large moths such as imperial and royal walnut moths from some of their former range.

I’d say the anecdote about wasps attacking the un-sleeved caterpillars isn’t really representative of their survival in nature. A concentration of a hundred caterpillars all giving off the scent of chewed leaves in the same place is a much more noticeable target than single caterpillars scattered around the trees.

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Well I guess that was sort of my point. Most paraistoids are more specialized than mantises and probably do more harm to their host species than mantises would because of that. And yes, many species that are heavily parasitized are still thriving but that doesn’t mean parasitism isn’t one of the leading cause of mortality for many of them.

Yes, I 100% agree that this isn’t representative of the wild at all but it does show that paper wasps can come in much larger numbers and and have the potential to do much more harm than mantises. There can be a dozen paper wasps circulating in an area whereas I doubt there’d be more than a few mantises per garden. I’ve also had many times where I would take just a single larva outside on a cutting to photograph and it could get killed by a paper wasp if I even let my guard down for a few minutes. Granted, I feel like the paper wasps are way more common in gardens than in the wild. When I sleeve saturniids on trees out in more remote areas the paper wasps are less of a problem but I’ve seen some very persistent ones investigating a sleeve for half an hour or so before finally giving up.

I believe our past success (in only the past 2-3 years) is because we are quite literally the only plot of cultivated native plants in a sea of asphalt, concrete, and commercial business/parking lots.

In 2015 we completely redesigned our backyard to create a meadow garden, woodland garden and cultivated hedgerow of native species; as a result we attracted monarchs…only in the last two years have we also attracted a variety of additional (new-to-our-property) species and now we are beginning to observe predation on the monarchs.

Essentially - prior to 2015 - we had a backyard full of invasive butterfly bushes that only appealed to nectaring adults.

Redesigning the entire property, and including swamp and common milkweed and butterfly weed we attracted monarchs and they were successful at first; the swallowtails came with the planting of fennel and until last year, they were also successful. To be clear: by successful I mean, the chrysalises I collected (snipped off the stem on which they made the chrysalis) and sheltered to eclosion were not parasitized (nor, obviously, consumed). I collected and sheltered all chrysalises in a screen-top aquarium and released butterflies semi-daily – nothing very scientific about it…just lining them up inside a sheltered place, waiting for them to eclose and then taking the aquarium outside and opening the lid to allow them to fly away (once their wings had dried). For the first few summers, we released about 20 monarchs…swallowtails were actually fewer…probably 10 or 12 per year.

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Your mantid situation may well be exactly due to the isolated and thus artificial nature of your backyard meadow. The butterflies may well be present at far more than natural population density on a small patch of flowers making them much more susceptible to mantises than in larger, natural areas with more spread out flowers.

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Exactly our fear. We feel terrible. We thought we were improving the habitat. One wonders why people are encouraged to create such artificial spaces if we only disrupt the natural order of things.

Even if there were some impacts, I think your effort is very laudable. Something more of us should consider doing.

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