This is about the time of the year that my attention turns to terrestrial flies and the spectacular hits that can be had. Webster’s definition of terrestrial is “living on or in or growing from land”. Basically, terrestrial insects are insects that are born on land and remain on land all their life unless they are blown into the water by wind or accidentally get into the water some other way. They probably don't have the intelligence to know that water is dangerous to their well being and just land there by chance as well as anywhere else. The most common terrestrial insects are ants, beetles, grasshoppers, crickets and moth larvae. There are several others.
Since this is an unseasonably warm year, many of the aquatic insects (insects born in the water) have hatched and are in the egg or tiny size nymphal or larval stage of their life. Such insects are Quill Gordons, Blue Quills, Hendricksons, Winter Stoneflies, Little Brown Stoneflies, Little Black Caddis and others. The list of food you see above will be reduced during the next month down to only a very few aquatic insects as compared to what the list is now.
This is the reason why terrestrial insects will become important soon. Another reason is that about this time of the year, the terrestrial insects have become adults and are far more subject to landing in the water than when they are immature. They are also large enough and provide enough food to get the trout's attention.
Obviously it isn't normal for a terrestrial insect to get into the water. Most of the time the moth larvae, and grasshoppers get into the water because they are blown in by high winds. Most of the ants and beetles that get in the water are washed in by heavy rainfall. Therefore, the kind of weather on any one particular day will determined you selection of terrestrial imitations.
We at Trout University have a good selection of terrestrial flies to choose from and they are what we believe are the best imitations of the insects available.