What is "gall insect"

Gall \Gall\ (g[add]l), n. [F. galle, noix de galle, fr. L. galla.] (Zo["o]l.) An excrescence of any form produced on any part of a plant by insects or their larvae. They are most commonly caused by small Hymenoptera and Diptera which puncture the bark and lay their eggs in the wounds. The larvae live within the galls. Some galls are due to aphids, mites, etc. See Gallnut.

Note: The galls, or gallnuts, of commerce are produced by insects of the genus Cynips, chiefly on an oak ( Quercus infectoria syn. Quercus Lusitanica) of Western Asia and Southern Europe. They contain much tannin, and are used in the manufacture of that article and for making ink and a black dye, as well as in medicine.

Gall insect (Zo["o]l.), any insect that produces galls.

Gall midge (Zo["o]l.), any small dipterous insect that produces galls.

Gall oak, the oak ( Quercus infectoria) which yields the galls of commerce.

Gall of glass, the neutral salt skimmed off from the surface of melted crown glass;- called also glass gall and sandiver.
--Ure.

Gall wasp. (Zo["o]l.) See Gallfly.