Dragonflies vs robber flies. Who eats who?

Dragonflies and robber flies are the best aerial predatory insect
I always wonder if this two insects hunt each other, then who eats who?

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I believe it depends on the size, medium dragondlies eat damselflies and also can eat small/medium robberflies. Big robberflies probably can hunt on small Odonata.

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robber fly wins. i’ve never seen a dragonfly eating a robber fly, but i have seen robber flies eating much larger dragonflies.

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We have two spiders species in NZ, white tail (Lampona) and daddy long legs (Pholcus phalangioides), and it’s common knowledge that the daddylonglegs eat the whitetails. However, if you actually look into it it’s more 50:50, and I think we only “notice” the Pholcus eating the Lampona more because the Pholcus wraps up the victim and consumes it over a long period of time, whereas the Lampona stalks, takes and eats it’s prey over a much shorter period of time, and then scarpers it to look for more prey.

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There’s an odonata as prey project. I added this observation to it today.

(There’s also a project for Odonata as predators)

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I’d say that robberflies are more formidable predators overall, especially for their size, but it probably also has a lot to do with which predator attacks the other first.

Robberflies usually have an ambush hunting style, where they sit on a perch and rarely fly except to briefly dart out and grab prey. Dragonflies capture virtually all of their prey in the air, so dragons don’t get as much opportunity to catch robberflies as robberflies get to grab dragonflies as they fly past.

Considering that green darners are known to take down large prey, such as other dragonflies as large as themselves and even hummingbirds (there’s a pic of one eating a hummingbird, google it), I bet that a green darner could prey on that giant Microstylum robberfly if it encountered the fly flying out in the open and attacked first…but robbers don’t often fly out in the open where dragonflies could spot them first and catch them.

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I have seen robber flies take dragonflies longer than themselves. As already mentioned, robber flies are ambush hunters while many dragonflies catch small prey on the wing (many dragonflies also perch and ambush). I was wondering if it had anything to do with musculature - like the quick-flex (power) muscles an ambusher might have (comparing with mammals) to the slow-flex (endurance) muscles of a constant flyer.

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I’m not sure if the muscles of insects are comparable to vertebrates in terms of quick/slow flex - i might have a bit of a look into that.

However, I have observed dragonflies and robber flies predating on each other a few times, but both ways only rarely. I would probably expect robber flies to catch and kill more dragonflies in absolute terms just because, as has been mentioned, dragonflies are predating on already flying insects, either while perching or hawking. However, I would expect dragonflies to catch and kill more robber flies as a % of attempts due to better manoeuvrability. I’m not sure if robber flies suffer from confusion but I know dragonflies don’t (At least the species i’ve studied.)

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Personally I’d say it goes both ways. Asilidae would take the opportunity to prey on Odonata if possible and certainly I can see Odonata feeding on smaller Asilidae too.

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In my experience from identifying 50k+ robber fly photos on iNat, robber flies take odonate prey relatively frequently, but I don’t think I have seen the reverse. Odonates preying on robber flies have been recorded in the literature, but my understanding is that it happens rarely.

I think @polypody has the correct explanation:

Robberflies usually have an ambush hunting style, where they sit on a perch and rarely fly except to briefly dart out and grab prey. Dragonflies capture virtually all of their prey in the air, so dragons don’t get as much opportunity to catch robberflies as robberflies get to grab dragonflies as they fly past.

The biggest threats to Asilidae are birds and other ambush hunters (like jumping spiders and fellow robber flies).

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Both of these projects are great compilations

Here are the 54 iNat observations that have been included so far of odonates being prey upon by robber flies. I’m not sure how to search Observation Fields for observations of asilids being preyed upon by odonates.

Another cool predator-predator interaction to consider – salticid vs odonate: https://www.inaturalist.org/observations/25969276

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I believe that the battle’s outcome depends on the first attack. The robber fly is an ambush predator, while the dragonfly quickly swoops in and kills it’s target. If the robber fly can grab the dragonfly, the robber flies’ long legs will give it the victory of this fight. But if the dragonfly hits one of the vulnerable parts of the robber fly, then it will have a swift and simple victory.

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I have nothing specific to add, except that this conversation is very fascinating! A person learns something new every day. Thank you all!

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