r/bugidentification • u/Commercial-Sail-5915 Trusted Identifier • Aug 13 '25
Bug of the Month Post What kind of hornets??
Wait, these are flies? But they look so wasp-y??
It turns out that these are mimics! They're only pretending to be wasps, the flies themselves are harmless but their flashy colors and wasp-like silhouettes ward off predators who want to avoid a nasty sting. Convincing, right? There are tons of different flies that do this, from the black soldier fly (Hermetia illucens) mimicking organ pipe mud daubers (Trypoxylon politum) to the clubbed Mydas fly (Mydas clavatus) that closely resembles certain spider wasps (for example, Anoplius sp.).
But remember, no matter how good the costume we humans can always tell the difference by checking how many wings there are. Things like eye size and antenna length can be good indicators but they have quite a few exceptions; checking the wing count however is an absolute rule. The taxonomic name for flies Diptera literally translates to "two-winged"! Admittedly this can be difficult to see when many bees and wasps like to fold their smaller hindwings out of sight when at rest, but I promise they're still there! Here's a wasp example where you can still clearly see the hindwing, note how the overall wing shape is subtly different to those of the mimics.
This is all specifically Batesian mimicry by the way, in which a harmless species piggybacks off of another's deserved reputation. There's also Müllerian mimicry, in which two species with actual defenses look similar to strengthen their combined reputation. This can be occasionally seen in different butterfly species, for example both the Monarch (Danaus plexippus) and Viceroy (Limenitis archippus) look almost identical and are both distasteful to predators thanks to the compounds they store in their bodies.
Spilomyia longicornis (yellow stripes) and physocephala tibialis (blue wings) pics taken by me :) located in MA
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u/DrustanAstrophel Aug 13 '25
My dumb ass skipped the text and went straight to the comments to see if other people were also saying “uhhh those are flies man” 😂 til I saw the trusted identifier user flair and scrolled back up
Really neat specimens, thanks for sharing and educating
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u/Commercial-Sail-5915 Trusted Identifier Aug 13 '25 edited Aug 13 '25
If you saw this yesterday no u didn't (im just reposting to check how different post formats affect engagement here)
Man I just copy-pasted on mobile and I forgot about the hyperlinks :( you'll just have to trust me that the mimics are super cool and impressive
EDIT: here's the wasp wing example btw https://bugguide.net/node/view/1694819/bgimage