Brauer (1863) divided the Diptera into two sub-orders[8]; of the first
of these a Crane-fly or 'Daddy-long-legs' may be taken as typical, of
the second an ordinary House-fly or Bluebottle. All the larvae of the
Diptera are legless, those of the Crane-fly group have well-developed
hard heads, with biting mandibles, but in the House-fly section the
larva is of the degraded _vermiculiform_ type known as the _maggot_,
not only legless, but without a definite head, the front end of the
creature usually tapering to the mouth, where there are a pair of strong
hooks, used for tearing up the food. A few examples of each of these
types must suffice in the present brief survey. A few pages back (p. 66)
reference was made to the production of galls on various plants, through
the activity of larvae of the hymenopterous family Cynipidae. Many
plant-galls are due, however, to the presence of grubs of tiny dipterous
insects, the Cecidomyidae or Gall-midges. A cecid grub (fig. 19) has an
elongate body with flexible, wrinkled cuticle, tapering somewhat at the
two ends. The head, if rather narrow, is distinct, and beneath the
prothorax is a characteristic sclerite known as the 'anchor process' or
'breast bone.' Along either side of the body is a series of paired
spiracles, each usually situated at the tip of a little tubular
outgrowth of the cuticle; the hindmost spiracles are often larger than
the others. These little grubs live in family communities, their
presence leading to some deformation of the plant that serves to shelter
them. A shrivelled fruit or an arrested and swollen shoot, such as may
be due respectively to the Pear-midge (_Diplosis pyrivora_) or the
Osier-midge (_Rhabdophaga heterobia_), is a frequent result of the
irritation set up by these little grubs. In a larva of the crane-fly
family (Tipulidae, fig. 20) living underground and eating plant-roots,
like the well-known 'leather-jacket' grubs of the large
'Daddy-long-legs' (Tipula) or burrowing into a rotting turnip or swollen
fungus, like the more slender grub of a 'Winter Gnat' (Trichocera), the