This is a bumble bee robber fly that was seen in the Nature Gardens at NHM. It was hanging out on the kangaroo paws in the garden on the east side of the building (the 1913 garden) right next to the bee hotel and the milkweed patch. It picks off wasps and bees, injects them with venom and digestive enzymes, and sucks them dry.
Photo and info courtesy of Brian Brown.
This spectacular photo was taken by David Sheehan in Westchester, CA.
The robber fly has injected this wasp with venom and digestive enzymes so it can drain the wasp of its bodily fluids.
Falcon State Park
Zapata Co., Texas
12 October 2004
(part of the park is in Zapata Co., but most of it is in Starr Co.)
Live Oak Creek,
Crockett Co., Texas
3 September 2013
\Identified as Efferia species by Herschel Raney on Bugguide.