Explanation of Names
From Latin ampulla, flask.
ampulla, plural ampullae - any membranous blister, vesicle, or similar structure on the surface of an insect.
ampulliform adjective - bottle-shaped; swollen; resembling an inflated bladder
For an example of the location and size of the greater ampulla as shown on a tachinid fly, see this illustration
on the NADS website ("gr amp" in complex lower right figure).