Large Robber Fly: Saropogon dispar

Subject:  Hairy wasp-like bug with some kind of oral stinger
Geographic location of the bug:  Southeast Texas, USA
Date: 07/08/2018
Time: 10:51 AM EDT
Your letter to the bugman:  I’ve been seeing these guys at my work which is a fracking site in the middle of a cattle ranch. I have seen about 5 of them but all separately, not in a group. They look like giant wasps, but they’re very hairy and have some kind of stinger out of their mouths. I may have seen a stinger out of the thorax as well but I’m not sure. And I have noticed multiple dead bug carcasses around the area, such as grasshoppers and beetles. I thought it might be relevant in case these bugs are like the wasps who lay parasitic eggs in paralyzed bugs.
Picture taken in July.
How you want your letter signed:  Dave

Robber Fly:  Saropogon dispar

Dear Dave,
This is a predatory Robber Fly, and Robber Flies frequently capture large flying insects that they feed upon, so the carcasses you have found might have been prey.  Like other Flies, Robber Flies do not chew prey.  They feed on the fluids, leaving a dried carcass behind.  We are having trouble matching your images to an exact species or even a genus.  Its most obvious diagnostic features are its long legs, white beard, black wings and striped abdomen.  It really resembles a Hanging Thief in the genus
Diogmites, but they are usually orange.  We did locate a dark Hanging Thief on BugGuide, Diogmites platypterus, and it has a white beard and black wings, but your individual lacks the orange legs.  Our best guess at this time is the enormous Microstylum morosum, pictured on BugGuide, but they don’t have white stripes on the abdomen.  Does your individual have green eyes?  That is difficult to discern in your images.  Prolepsis tristis pictured on BugGuide also looks similar, but lacks the diagnostic white beard.  We have written to Eric Eaton for assistance.  For now, we are certain this is a predatory Robber Fly in the family Asilidae, and we hope to have a more specific identification for you soon.  Perhaps our readers will be able to assist.

Robber Fly:  Saropogon dispar

Thanks for the response! Yes the eyes were a dark green color. And it was very large, I approximate it to be 1.5-2 inches long. The Microstylum morosum looks like the closest match to me except for that abdomen and the bright green eyes. I didn’t know anything like this family of insects existed!

If it is indeed Microstylum morosum, it is the largest Robber Fly in North America.

Eric Eaton Responds
Ok, I submitted to the Facebook group, but then looked at the website for robber flies of Arkansas and may have found it:  Saropogon dispar
author, Kaufman Field Guide to Insects of North America

Thanks so much Eric.  We looked it up on BugGuide and Saropogon dispar sure does look correct.

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