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XIII. The Galls of Essex ; A Contribution to a List of
the Insect Fauna of the County.
By Edward A. Fitch, F.L.S., Sec. Ent. Soc, &c,
Vice-President.
[Read October 29th, 1881.]
A gall may be defined as an abnormal or morbid growth,
due to parenchymatous hypertrophy, and produced by the
peculiar action of some unnatural or foreign agency, probably
through mechanical irritation. These growths occur both in
the animal and vegetable kingdoms. Animal galls are not
common, unless we include the various inflammatory growths
and excessive developments of cuticle so common in the
Mammalia, which are gall-like in nature, although not true
galls. Animal galls caused by insects, however, occur in the
peculiar "worbles" or "bots" often so commonly seen on
the backs of our young cattle; these are produced by a
dipterous fly (OEstrus bovis, Linn.), which lays its eggs under
the skin of the bullock, and the inflammation set up produces
a gall in which the larva resides until full-fed.1 This is
hardly a true gall, as there is a small orifice communicating
with the open air, but still it is as analogous as the exigencies
of animal and vegetable pathology will allow. Animal
pseudo-galls have also been produced by the action of various
Acaridea. Much of interest might be said about these and
other pseudo-galls ; but our business is with the vegetable
galls more particularly, and to these we will turn.
Plant galls are fairly ubiquitous, and some kinds must be
known at least by sight to everyone ; these distinct abnormal
growths have been noticed by all naturalists or general
observers in one form or another, especially the galls occurring
on various trees, as the oak, willow, elm, or rose.
1 Many similar swellings are produced on various animals by the
OEstridae. Cf. F. Brauer's 'Iconographie der OEstriden.' Vienna, 1863.