It is an easy meal for a trout. Spider patterns are always a good standby to attract the larger trout. These terrestrials can be swept away current as the build their webs on over hanging riverbank plants. In the evenings of mid spring to early summer the water surface can be littered with the fallen mature mayfly spinners. Other groups of insects go through a similar sort of development and form part of the trout's diet.
Midges develop from bloodworm lava stages to pupa and then adult.
Caddis and sedge flies lava is encased for protection before it develops into it's pupa stage and then into the adult. Terrestrials like ants and grass hoppers are also gobbled up if they fall into the water.