Filariasis: a disease caused by the presence of minute worms or Filaria, transmitted by mosquitoes. {Scanner's comment: Nowadays it is known that many kinds of filariasis are transmitted by other species of flies, in particular Simuliidae and Tabanidae}
Filate: Diptera; antennae that are simple, without lateral hair or dilation: thread-like.
Filator: the silk spinning structure of caterpillars.
File: the diagonal ridged vein near the base of the tegmina in crickets, used in stridulating: in general any structure wherever situated that serves the same purpose.
Filicornia: insects with thread-like antennae; e.g. in Coleopteran, the Carabidae.
Filiform: thread-like: slender and of equal diameter.
Filippi's glands: a pair of secondary glands, opening into the silk glands of caterpillars near their anterior end.
Fillet: a transverse, raised structure between the antennae in Lepidoptera.
Filose: ending in a thread-like process.
Fimbria: thick, ciliated hair at the termination of any part: fringes.