The members of this group are the insects commonly known as Caddis
Flies, and they are often ranked as a separate order by entomological
writers.
Nearly 600 species of _Trichoptera_ occur in Europe, of which about
half the number are indigenous to the British Isles. The _larvæ_ are
aquatic, and when full-grown prepare for themselves curious dwellings
composed of sticks, stones, and other materials wherein to pass the
pupa state. They may be seen almost everywhere where there is water.
The caddis flies may be divided into two families, though the
distinguishing marks are so minute that they really ought to be
classified as one family only. To Mr. McLachlan we owe many thanks for
his researches in this group of insects.
[Illustration: Fig. 52.--Hydropsyche Montana.]
[Illustration: Fig. 53.--Marronema Rubiginosa.]
_Family 1, Inæguipalpia._--This family includes the largest species of
the tribe, and are principally found in northern regions.
One of our largest British species is _Phryganea grandis_, which
measures four-fifths of an inch in length, and over two inches in
expanse of the wing. It is an abundant insect, of a brown colour, with
yellow rings on its _antennæ_, and the anterior wings are ash-coloured,
clothed with brown.
The _larvæ_ of this group for the most part inhabit quiet waters,
ponds, canals, etc.
This family is subdivided into three sub-families, viz., _Phryganeidæ_,
_Limnophilidæ_, _Sericostomidæ_.
_Family 2, Æguipalpia._--This family constitutes a second group, and
also contains many species, many of them, however, being very minute
insects, some hardly one-eighth of an inch across the wings. They make
little cases of silk resembling seeds, to the outer surface of which
they attach grains of sand, etc.
The _Æguipalpia_ contains four sub-families--viz., _Leptoceridæ_,
_Hydropsychidæ_, _Rhyacophilidæ_, and _Hydroptilidæ_.
Of the _Leptoceridæ_, _Molanna augustata_ may be taken as a typical
example, the larva of which lives on the sandy bottom of pools, and is
very difficult to detect.