What Fish Eat
Aquatic insects make up the majority of a fish's diet. The four key insect orders (listed first and not including Streamers or Terrestrials) that emerge from streams and lakes are:
Terrestrial insects such as ants, beetles, and grasshoppers make up a significant portion of a freshwater trout's diet. Don't under estimate the effectiveness of terrestrials even when aquatic insects appear in good numbers.
When and Where to Fish Terrestrials
Early in the season, winged queen and male ants take to the air in search of a location to start a new colony. The combination of gusty winds and their fragile wings can put them on the water surface where trout will gorge on them. Starting around mid July, grasshoppers appear throughout the Sierra Nevada. Their numbers vary thoughout the Summer months, however, trout tend to key on them later in the season as available aquatic hatches decrease. As for beetles, it's rare to find them on the water in large numbers, but a sufficeint number are blown onto the water throughout a season to keep trout interested.
Work terrestrial patterns near overhanging grass and brush, especially when the wind is blowing insects into the water. When fishing beetle patterns, don't limit your presentations to the water along the blank. As beetles are fliers, they can put down in the middle of the stream as well as the edge along the blank.
Photo of October Caddisfly by P. Michael Carl © The Ecological Angler