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Robberfly species? - Promachus vertebratus

Robberfly species? - Promachus vertebratus
West Chicago Prairie, Cook County, Illinois, USA
August 31, 2004
Not sure what species...anyone have an idea?

Moved from Giant Robber Flies.

Robber Fly
I'd venture to say Promachus vertebratus; I've photographed the same fly numerous times at Winfield Mounds Forest Preserve, just a few miles east of the West Chicago Prairie. Huge green eyes, lumbering, buzzing flight - a magnificent beast! Please see my photos at

Likely vertebratus and rufipes occur in that area and both have the yellow and black abdominal banding. They are large predators. I have a shot of our species P hinei, that is similar, after it took an adult Halloween Pennant. These and Triorla are the only robbers I have seen take adult dragonflies.

Need more clues:-)
If it was pretty large (inch or more), it is probably a species of Promachus. It is a female, we can tell by the tapered abdomen. Male robber flies have enormous claspers at the end of the abdomen.

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