240 Nerve-winged Insects; Scorpion-flies; Caddis-flies 
heavy spruce forests, and the strange aquatic larvae desperately clinging 
to the smooth boulders and rock bed of the swift mountain streams are 
among the most interesting and prized of all the insect host. So it was 
that my first summer’s camping and climbing in the Rockies acquired a 
special interest from the slight acquaintanceship I then made with a group 
of insects which, unfortunately, are so little known and studied in this 
country that the amateur has practically no written help at all to enable 
Fig. 330 .—Leptocerus resurgens. (After Needham; enlarged.) 
him to become acquainted with their different kinds. These insects are 
the caddis-flies; not limited in their distribution by any means to the Rocky 
Mountains, but found all over the country where there are streams. But 
it is in mountain streams that the caddis-flies become conspicuous by their 
own abundance and by the scarcity of other kinds of insects. 
In Europe the caddis-flies have been pretty well studied and more than 
500 kinds are known. In this country about 150 kinds have been deter¬ 
mined, but these are only a fraction of the species which really occur here. 
Popularly the adults are hardly known at all, the knowledge of the group 
being almost restricted to the aquatic larvae, whose cleverly built protecting 
cases or houses made of sand, pebbles, or bits of wood held together with 
silken threads give the insects their common name, i.e., case- or caddis- 
worms. The name of the caddis-fly order is Trichoptera. 
These cases are familiar objects in most clear streams and ponds. 
Figures 331 and 332 show several kinds. There is great variety in the 
materials used and in the size and shape of the cases, each kind of caddis- 
worm having a particular and constant style of house-building. Grains 
of sand may be fastened together to form tiny, smooth-walled, symmetrical 
cornucopias, or small stones to form larger, rough-walled, irregular cylinders. 
Small bits of twigs or pine-needles may be used; and these chips may be 
