Anacharoides, usda nmh buffington

This is picture 2 from a 12 picture invited series by Matt Buffington at the USDA Parastitic Hymentoptera group using specimens from the U.S. Natural History Museum Smithsonian. Matt uses a system very similar to ours to photograph and stack this super tiny wasp. This native of the Rift Valley in Africa is called Anacharoides. Like Aspicera, these wasps attacked aphid-feeding syrphid larvae. However, we don't know what the peculiar protrusion on the top of the wasp is for defense, perhaps?