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OAK GALLS AND GALL INSECTS
There are also insects of various orders which feed upon the
substance of the larger galls such as Biorhiza terminalis. They
are known as "commensals."
On account of the number of parasites, inquilines, etc.,
found in oak galls, it is important to differentiate between them
and the true gall-makers :—
Fig. 1. Wing of a Chalcid.
Characters of the Chalcididae. Wings without a system of cells, having a
single nervure proceeding from the base near the costa to which it afterwards
passes after giving off a short vein more or less terminally thickened.
(Fig. 1.) The angles of the pronotum do not extend back to the point of
insertion of the tront wings. Antennae elbowed, with seven to thirteen joints.
Fig. 2 A. Wing of an Ichneumonid.
B. Wing of a Brachonid
Characters of the Ichneumonidae. Wings with a system of cells well
developed. The space in the front wing dividing the posterior cell from the
cubital cells, is separated into two portions by a transverse veinlet. (Fig. 2 A.
Antennae many jointed. Abdomen attached to the lower part of the medium
segment,