1914] Biology of Net-Spinning Trichoptera 265. 
III. THE AQUATIC SITUATION. 
All of my collecting and observations on the net-spinning 
Trichoptera were confined to a very limited area in Casca- 
dilla Creek, not exceeding a half mile in extent. For a pre- 
liminary study this presented advantages, one of the most 
important being an abundance of material within a few min- 
utes walk from the laboratory. This made it possible to ob- 
serve conditions frequently and to spend more time in the field 
than would have been possible had the Creek been at a distance. 
The use of the Fish Hatchery, situated on the bank of the Creek, 
also offered opportunities for studying things to the best ad- 
vantage, for all necessary equipment as microscopes, instru- 
ments and glassware could be kept there. It also furnished a 
place where rearing and experimental work might be carried 
on, undisturbed and under natural conditions. 
The depth of the Creek varies from a few inches, where it 
spreads over the large, flat rocks, to two and a half feet or 
more in the middle of the stream. The creek-bed averages. 
from ten to fifteen feet in width but broadens out in places to 
thirty feet or more, where the larve abound, the bottom is rocky 
and of two types—loose stones, both large and small, (See Plate 
XXXVI, Photo 1), and continuous shelving rocks with gradual 
descents of a few inches to steep descents of five feet or more. 
(See Plate XXXVI, Photo 2). In early spring and fall the 
water rushes along in torrents over the rocks, but by midsum- 
mer the swift water is confined to the middle of the creek-bed. 
Large areas of the broad, shelving rocks remain dry and where 
there is water it does not exceed an inch in depth. 
Most of the typical swift-water forms of insect nymphs. 
and larve were found associated with the Hydropsychids. 
Of the Trichoptera, Rhyacophila, Helicopsyche, Silo, and a 
Hydroptilid sp.; of the Diptera, Simulium, Chironomid and 
Blepharocera larve were very abundant on the upper surface 
of the stones; of the Mayflies and Stoneflies, the nymphs of 
Heptagenia, Chirotonetes and Neoperla were found in numbers. 
on the under side of the stones. The rocks presented various 
colors—the browns of diatom ooze, large black patches of Simu- 
ium larve, and in places thick green carpets of Cladophora. 
The swift water and great abundance of food made it an ideal. 
situation for the larve. 
