A calypter is either of two posterior lobes of the posterior margin of the forewing

Insect wing

Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...

 of flies

Fly

True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...

 between the extreme posterior wing base and the alula

Alula

The alula, or bastard wing, is a small projection on the anterior edge of the wing of modern birds. The alula is the freely moving first digit, a bird's "thumb," and is typically covered with three to five small feathers, with the exact number depending on the species...

, which covers the halteres.

The lower calypter is the proximal calypter (synonyms: squama (of some authors), tegula ) and the upper calypter is the distal calypter (synonym: squamula).

Species of the subsection Acalyptratae

Acalyptratae

Acalyptratae is a subsection of Schizophora, commonly referred to as the acalyptrate muscoids . It is a very large assemblage, exhibiting very diverse habits, with one notable and perhaps surprising exception; there are no known acalyptrates that are obligate blood-feeders , though this is a life...

are noted for lacking calypters.