134 The Galls of Essex ; a Contribution to a
branches of trees. They are hard, conical, single-celled
galls, coarsely furrowed on their basal two-thirds. They
never occur singly, and when fresh the galls are deep red in
Fig. 19. Aphilothrix Sieboldii.
colour, which tint they lose after the emergence of the insect.
The galls are mature in September, and the gall-flies emerge
therefrom in April or May. Aphilothrix Sieboldii, Hartig
(Fig. 19) [agamous form of Andricus testaceipes] .
Quercus Robur, L. Stem. The
galls are soft, succulent and berry-
like, occurring on the trunks of
young oaks. They are spherical,
pea-sized, bright red or yellowish,
and single-celled. The galls,

which mature very quickly, really

Fu:;. 20. Trigonatpis megaptera.
occur on the stem-buds of the
oaks in the spring ; they soon shrivel up and disappear after
the emergence of the gall-fly, which takes place in June.
Trigonaspis megaptera, Panzer. (Fig. 20).
Quercus Robur, L. Twig. Little, glabrous, oval swellings
are frequently noticeable on the bark of oak-twigs, more
especially when pierced by the gall-flies; these are the galls
of Andricus noduli. This single-celled gall also occurs on