Fossula -ae: a deep groove or sinus with sharp edges: specifically applied to grooves on the head or sides of prothorax in which the antennae are concealed.
Fossulate: a surface with oblong impressions.
Fossulet: an elongated, shallow groove.
Fourth longitudinal vein: Diptera (Will.), = media 2 (Comst.).
Fovea, Foveola -ae: a shallow depression with well-marked sides: a pit.
Foveate: with foveae or pit-like depressions.
Foveolate: with shallow cavities like a honey-comb.
Fractus: broken: also applied to a geniculate antenna.
Fragile: easily breakable: thin and brittle.
Frass: the excrement; usually the excreted pellets of caterpillars.