Monday, June 13, 2022

A cool robberfly, and a doppelganger

As always, click the photo to enlarge

You would not want to be a lesser bug and see this thing looking your way. It is one of the bumble bee-mimicking robberflies (Laphria thoracica [I should caveat my specific identity to say that I think it's that species. There are a few very similar Laphria species, and if I got it wrong, please let me know]). These large, highly predatory flies light out after flying insects, envelop them in an iron maiden death clutch, and administer the coup de grace with a syringe-like proboscis. Powerful neurotoxins are pumped into the victim, immobilizing it while other chemicals accelerate deterioration of the innards. The robberfly then sucks out the slush, using the proboscis as a drinking straw. All that'll be left is a withered husk.

I visited the legendary Cedar Bog last Friday, June 10, mostly to catch the end of the blooming of one of North America's most stunning orchid, the Showy Lady's-slipper (Cypripedium reginae). But there is always a wealth of subjects on display, and one I was watching for was the above robberfly. I saw a few, and as always had to try for some imagery.

Here's the robberfly in profile. Most anyone, upon seeing one of the bumble bee mimic robberflies in the genus Laphria, would think them to be just that - a bumble bee. But upon inspection, something isn't right, starting with their habit of sitting out in the open. A closer inspection reveals that the fly often quickly twists and tilts its head as it watches for potential victims. The remarkable mimicry may have evolved to give the predatory fly a measure of protection as it sits on its conspicuous perches. Many birds, notably excepting the Summer Tanager, probably learn to avoid big bugs that look like this. They don't want to get stung.

This insect was "hunting" in close proximity to the second robberfly that I located. And does it ever look like a robberfly, and acts very similar as well. But it is a type of flower fly in the vast family Syrphidae: the Orangeback (Pterallastes thoracicus). Flower flies are not predatory to my knowledge, instead living up to their name and visiting flowers for nectar and pollen. But boy, do the Orangebacks ever act the part of robberflies. They sit atop leaves, and make frequent loud buzzing flights as if they are after something. There is an aggressive element to them, and this one even strafed the significantly larger legitimate robberfly perched nearby. Perhaps its coloration, structure and habits are mimicry of the fearsome robberflies, although I don't know this for sure.

In an admittedly brief search, I could find next to no information about the Orangeback. I did learn that it apparently is rather uncommon and local. In the vast and ever-growing iNaturalist archives, there are only scattered - often widely so - records across the eastern U.S. They seem to become more common eastward and there are only about 30 Ohio records, mostly in the northeastern corner of the state. As conspicuous and easily seen as this insect is, there would no doubt be far more iNaturalist records if Orangebacks were everywhere. I pay more than casual attention to most insects, and I've only seen this species once before, in 2020, also at Cedar Bog.

If you know anything about the Orangeback and perhaps have some good sources to learn more, please pass them along.

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