132 The Galls of Essex; a Contribution to a
behind (when mature they fall at the least touch). There
are generally eight or ten galls on a leaf, occurring on each
side of the midrib, mostly in the angle of a side vein. The
larva lives in the gall throughout the winter, pupating therein
in the spring. Hormomyia piligera, H. Loew.
Quercus Robur, L. Root-
lets. The galls when single
are about as large as a hazel
nut, but they generally occur
in confused masses of five or
six together. The galls are
soft when recent, but soon be-
come hard and woody ; they
are round, oval, or reniform
pyriform when confluent, and
contain from three to nine
thin-walled, oval larva-cells,
which are yellowish on the
inside. The galls are mature
in the autumn, and the apte-

rous, ant-like gall-flies emerge

Fig. 16. Biorhiza aptera.
therefrom throughout the win-
ter. Biorhiza aptera, Fabricius (Fig. 16) [agamous form of
Andricus (Biorhiza) terminalis] .
Quercus Robur, L. Root. This gall generally occurs just
below the surface, where the roots leave the trunk, and is
mostly, considerably larger than the preceding. It is round,
rough, hard, and woody, varying in colour with the surrounding
soil from light yellow or reddish to almost black ; it somewhat
resembles a truffle. In section the gall shows numerous oval
larva-cells embedded in its parenchyma. The gall is mature
in autumn, and the gall-flies emerge therefrom in April.
Aphilothrix radicis, Fabricius (Fig. 17) [agamous form of
Andricus noduli] .
Quercus Robur, L. Bark. The gall is tooth- or rather
nail-like in shape, and is found deeply embedded in the
trunks of old oaks, frequently on the bark encircling the spot
where a large branch has been removed on old pollards.