118 The Galls of Essex; a Contribution to a
British species are known to produce galls, and many of these
are amongst our most familiar ones,—e. g., the dewberry-stem
gall, the willow rose-gall, the beautiful little purse-like gall
on the leaves of the meadow-sweet, the ground-ivy leaf-gall,
the shining yellow and red nodules on the stems of the bed-
straw, &c.; but as I have lately given a synopsis of the
British species in the 'Entomologist,'40 I must refer the
reader to that paper for information respecting such species
as have not yet been found in our county. Most of the galls
made by the Cecidomyidae are especially noticeable, and, as
I have said, many are quite familiar to us; still the gall-
gnats themselves are very small, obscure, and easily over-
looked by the general naturalist, although a specialist writes
of them, "these flies (Cecidomyidae) are the most elegant
and delicate little creatures in the whole of the Diptera."
Their life-history is very varied, and as the nature of their
metamorphosis is of consequence when breeding the flies, so
that the student may know whether they pupate in the gall
or otherwise, I have noticed this in the table of species.
Another family of the great order Diptera—the Trypetidae,
whose economy is so especially interesting to the phytologic
entomologist—includes a few gall-makers, besides numerous
leaf-miners, leaf-blotchers, flower-feeders and fruit-feeders.
The bright-coloured, spotted and banded winged, flies are
objects of especial beauty, and are easy of specific arrange-
ment. The galls produced by them nearly all occur in the
seed-capsules and flower-heads of various Compositae, and are
therefore not very noticeable, but the well-known thistle-stem
gall of Urophora Cardui is an exception. The Trypetidae
pupate within the galls. Two or three other fly-galls are
known, but they call for no especial remarks, except their
diversity of habits from their congeners, so we will pass on
to the Aphis galls, about which I must also be very brief,
although they really deserve a separate paper. The pine-
apple-like fir galls and elm and poplar leaf-galls are familiar
examples of their productions, but their economy is especially
involved and obscure. The interesting biological questions
40 'Entomologist' xiii, 146—154 (July, 1880).