142 The Galls of Essex; a Contribution to a
they do not become detached from the leaf. The gall-fly
emerges from the gall in October and November. Dryophanta
divisa, Hartig (Fig. 35) [agamous form of Spathegaster
verrucosa] .
Quercus Robur, L. Leaf. Galls very similar to those
last described are frequently found on the under side
of the oak leaf, but only singly, and they are not smooth,
but mostly covered with irregular nodules. In section
they also exhibit very thin walls to the larva-cell, and
are generally considerably smaller than the galls of
D. divisa, and are not so brightly coloured. The gall
is mature in early autumn, and the gall-flies emerge
therefrom in October. Dryophanta agama, Hartig (see
Fig. 85a), sexual form unknown.
Quercus Robur, L. Leaf. The
common "silk-button" galls oc-
cur in numbers on the under
side of the leaf, to which they
are attached by a very minute
foot-stalk; the gall is round,
with a depression in the centre,
and its surface is covered with Fig. 36. Neuroterus numismatis,
smooth, silky, brown hair ; hence
its popular name from its resemblance to a brown, silk-
covered button. When mature it has a diameter of about
the eighth of an inch ; it falls to the ground in the autumn,
and the larva feeds and grows in the single larva-cell
throughout the winter; the gall-fly leaves the gall in March.
Neuroterus numismatis, Olivier (Fig. 36) [agamous form of
Spathegaster vesicatrix] .
Quercus Robur, L. Leaf. These galls occur in numbers
on the under side of the leaf as almost flat, circular discs,
yellowish in colour, but their upper surface is covered with
short, reddish-brown, stellate hairs. They are commonly
known as the "oak spangles." The galls fall from the leaf
in autumn. When mature they measure about one quarter .
of an inch in diameter; the larvae feed and change to pupae
during winter, and the gall-flies emerge from the galls in