Promachus vertebratus

This species is the most common member of this genus in Wisconsin. They are very obvious when flying as they make lots of noise when flying and when mated this species may be seen flying ten feet high over the grasslands. It is easy to see them spinning somewhat out-of-control as it is not clear who is leading as they seem to spin or somersault as they fly.

Identifying characteristics

A large robber fly with mainly green eyes but sometimes with some red. The tibias are orangish but are somewhat variable and sometimes have small hairs that obscure the tibias and other times the tibias are brilliant orange as in the photo taken on July 23, 2007. The abdomen is light with contrasting dark marks on each abdominal segment.

Similar species

The other Promachus species are similar in size but really shouldn’t be mistaken for this species. Males of P. fitchii and P. bastardii have white-tipped abdomens and both sexes of these two species lack the obvious contrasting dark marks on each segment of the abdomen.

Habitat

Open grassland areas, including disturbed areas and old farmsteads.

Flight

Mid-July until early September.

Abundance

Not especially abundant but it is hard to miss this species when in prime flight because of how noisy they are when disturbed.

Locations

Map showing sighting locations for Promachus vertebratus
Map key
Promachus vertebratusClick to enlarge

Promachus vertebratus female

Muir Park SNA, August 4, 2002.

Promachus vertebratusClick to enlarge

Promachus vertebratus male

Baxter Lane, Lower Wisconsin River, August 8, 2008.

Promachus vertebratusClick to enlarge

Promachus vertebratus male with prey (bombus sp.)

Buena Vista Marsh, August 17, 2005.

Promachus vertebratusClick to enlarge

Promachus vertebratus male

Buena Vista Marsh, July 23, 2007.