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Mydas fly

I don't mean to be too heavy on the flies of late, but this one is just too cool not to plug. Besides, I've seen a few of these gnarly jumbos lately, and it may be a good year for them, for whatever reasons. If you see one of these giants, I guarantee you'll notice it.

BIG bug, on the corner of the headstone

I'm on the board of Columbus' Green Lawn Cemetery, which is one of Ohio's oldest (founded 1848) and second largest (360 acres). We manage it as an arboretum and park, which is how I came to be one of the board members. Some of the state's oldest and largest trees can be found, and about 90% of the native trees in Ohio are present. We've planted a three acre prairie, and there is a lush butterfly garden. Quite the urban oasis, a legendary birding locale, and teeming with all manner of wildlife.

I was in Green Lawn today, helping our general manager, Linda Burkey, give a tour to Patty Toneff of Toledo's Woodlawn Cemetery (another famous birding spot). We were slowly cruising along on one of the cemetery's 25 miles of roads when I saw a VERY large insect make a brief flight and come to rest at the base of a headstone. Fortunately, the women were tolerant enough to allow me a moment to leap out, grab the Nikon, and make some images.

Well, out I shot, camera in hand. The insect was not overly intimidated and allowed me to creep ever closer. I knew it was - or at least was fairly certain - some kind of fly, but the others that I had seen in the past week did not cooperate and no photos were made. So, I hadn't yet pinned a name on the beast. It acted rather territorial, flying to a few favored perches and acting as if it were guarding this particular piece of turf. It turns out that it probably was.

It was easy to make the identification once I returned to resources: mydas fly, Mydas clavatus, and it is indeed a robber fly looking thing. These animals are really big, comparable to our largest wasps. And indeed, it is a wasp mimic, trying to look like the big wasps in the Pompilidae family, and it resembles some of those species to an eerie degree. They even dangle their legs in flight, like wasps do.

So, as with the bumblee mimic robber fly that I recently posted about, this mimicry begs the question WHY? It turns out that in this case, the fly probably looks just like one of the large heavyweight stinging toughs so that other predators leave it alone. Tangle with a giant insect that packs a heckuva sting once or twice, and any bug-eating predator may learn to give them a wide berth. Presumably the mydas fly cashes in on this wasp world respect with its charade, and everyone leaves it alone as well. Except, probably, Summer Tanagers which dearly love huge ferocious bees and wasps and probably snap these mimics up as well.

Apparently adults will establish favored territories which they guard from other mydas flies, and that's what the one in these photos seemed to be doing. Interestingly, adult mydas flies are not thought to be predacious as are nearly all of their robber fly lookalikes. Instead, the adults seek nectar at flowers. The larvae are not pacifists though, and snack on beetle grubs in the soil or rotting wood.


Scott said…
I took a picture of one of these at the Midwest Native Plants Conference down near where we saw the Silver Spotted Skipper caterpillars. It was on a flower after nectar, kind of ruins the big nasty wasp image when it's on a flower.
Robbin buvk said…
I just came across your blog. I was excited to learn that the Mydas Fly is not dangerous. For the past 4 summers we have been chased off our deck by these Mydas Flies. We definitely have a pair here. They don't seem to chase each other or become territorial when the other one is around. We do have a few old stupms as well as raspberries, blackberries and strawberries growing near the deck as well. They don't care if your are human or mamal..they will chase you. I have watched the shiny black one land on a leaf and do the jabbing motion but see no stinger. Just glad to know that they aren't dangerous. Thanks for the info.

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