Frontal tubercles: in certain Aphids, are raised structures upon which the antennae are placed.
Frontal triangle: Diptera; the triangular space in males, between the eyes below, limited by a line drawn through base of antennae.
Frontal vesicle: in Odonata; that elevated area on the vertex upon which the ocelli are situated.
Fronto-orbital bristles: in Diptera; are placed on each side of the front, just below the vertical bristles.
Fugitive: soon disappearing; not permanent.
Fulcrant: the trochanter when continued along the femur, as in Carabids.
Fulcrum: the chitinous envelope at the base of mouth in Diptera and Hymenoptera, covering the beginning of the oesophagus: any structure that serves as a support to another..
Fulgidus: shining.
Fuliginous -osus: sooty or smoky brown [Van Dyke brown + a little black].
Fulvo-aeneous: brazen, with a touch of brownish yellow [brown pink].