The halteres of flies are the small club shaped structures that are located where you might find rear wings on some other insects. (Flies only have one set of wings for flight.) They are quite prominent on this large cranefly. They are usually refered to as the "vestigial" or "rudimentary" rear wings. They serve as "gyroscopes" or balancers during flight. Interestingly, research has shown that (at least on some flies studied) they also receive the flight directing stimuli from the insects vision rather than that stimuli going directly to flight muscles, as might be expected. If this is of any interest you should read this link:
http://www.berkeley.edu/news/media/rele ... 9_98a.html
