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Photo#1083367
Small-headed Fly. - Pterodontia johnsoni

Small-headed Fly. - Pterodontia johnsoni
Santa Cruz, Santa Cruz County, California, USA
June 12, 2015
Size: 4mm
Haltere?

Images of this individual: tag all
Small-headed Fly. - Pterodontia johnsoni - female Small-headed Fly. - Pterodontia johnsoni - female Small-headed Fly. - Pterodontia johnsoni Small-headed Fly. - Pterodontia johnsoni Small-headed Fly. - Pterodontia johnsoni

Moved
Moved from Small-headed Flies.

Those interesting hairy, transparent disks
...attached under the wing bases and seen edge-on in the photo above, are called the "(lower) calypters" or "squamae" (plural). They're unusually large and conspicuous in acrocerids.

The halteres are knob-like structures at the ends of short stalks, and are attached to the metathorax underneath the calypters. The two halteres are vestiges of the hind wings in Diptera. It's thought (or perhaps known) that they spin very rapidly during flight, and function somewhat like a pair of gyroscopes...helping flies maintain precise awareness of their overall orientation as the whiz through 3-dimensional space, and contributing to their acrobatic aerial abilities.

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