148 The Galls of Essex; a Contribution to a
fleshy and thick, probably belong to a closely-allied, but
distinct species.
Salix alba, L. Leaf. The margins
of the leaves are twisted and consider-
ably thickened. This pseudo-gall is the
work of the larva of Cecidomyia clausilia,
Bremi. (Fig. 49.)
Salix alba, L. Terminal leaves. The
willow "rose-gall" is too well known to
need detailed description, but it is more
than probable that we have two or three
closely-allied species whose respective
galls are not clearly differentiated. The
common form is the well-known tuft of
terminal leaves or leaf-rosette which is
so conspicuous an object at the end of
the twigs of our common pollard and
other willows, especially so on the bare
twigs during winter. The gall consists
of an imbricate mass of shortened, sessile,
and crowded leaves; in the centre is a

small, hard, inner gall, which contains
one or more larvae of the gall-gnat; the

Fig. 49.
Cecidomyia clausilia.
larvae pupate within the gall in spring,
and the imagos emerge therefrom in May or June. Ceci-
domyia rosaria, H. Loew. Similar galls occur on S. fragilis,
S. Caprea, and other willows.
Salix Caprea, L. Twigs. More or less globular, woody
swellings of the twigs of this sallow are frequently noticeable :
these are commonly the work of the gall-gnat mentioned
below, but more rarely of a sawfly; these latter most com-
monly occur on older twigs than the former. More than one
larva occur in the galls; they pupate therein in thin brown
cocoons in April, and the sawflies emerge therefrom in May
and June. Cryptocampus pentandrae, Retzius.
Salix Caprea, L. Twigs. The commonly found hard,
woody, irregular, and variable swellings of the twigs of the
sallow and other willow species are the work of gall-gnats.