The insects belonging to the third tribe of the Hymenoptera are
strictly vegetable feeders. There are only two families.
_Family 25, Siricidæ._--This family includes the insects known as
Tailed Wasps. It is not a very extensive family, and its species occur
chiefly in Europe and North America, in both of which regions the
typical genus _Sirex_ is represented by large species.
The best-known European species which is common in some parts
of Britain is the great Tailed Wasp (_Sirex gigas_), a very
formidable-looking insect, of which the female often measures nearly an
inch and a half in length.
[Illustration: Fig. 38.--Cimbex Luteus.]
The general tint is black with the antennæ, the sides of the thorax and
the legs and apex of the abdomen yellow. This insect lives in pine and
fir woods, and the female deposits her eggs in the woody parts of the
trees, into which she bores to a depth of over half an inch by means of
her long ovipositor.
[Illustration: Fig. 39.--Lophryus Pini (Mag.)]
[Illustration: Fig. 40.--Pamphilius Faustus (Mag.)]
Another species which occurs in this country is the _Sirex juvencus_,
of a steel-blue colour, but smaller than the former.
_Family 26, Tenthredinidæ._--This is a very extensive family and
contains the numerous species of Saw Flies, so called because their
ovipositor is in shape somewhat like a saw in appearance.
Probably the best-known species is the Gooseberry Saw Fly (_Nematus
ventricosus_), whose speckled and green _larvæ_ are so injurious in
gardens and orchards. This insect is yellowish in colour, and about a
quarter of an inch in length.
_Tenthredo æthiops_, a small black species, deposits its eggs upon
fruit trees.
Many other species live on different kinds of plants and trees.