Quote Originally Posted by DruLeeParsec
OK, I tend to see and hear splashes and I see them jumping out of the water. So that should mean that they're feeding on surface bugs.
No
It means they're chasing something that is moving quickly

Unlike most mayflies that might need a few tries to break the surface tension, then a bit of time to climb out of their exoskeletons, then take some more time to dry their wings and maybe have a cup of coffee before taking flight, caddis emerge as adults from their casings on the stream bottom. They make a beeline for the surface, break the surface tension, and get the hell out of Dodge.
There are some adult caddis that lay their eggs on the stream bottom. These bugs are diving not emerging, but still are speedy and trout chase them
Other caddis lay their eggs on the surface.
These bugs flutter around all over the place and trout will of course slash at them too
(trout will also slash at egg laying mayflies in the same manner)
A trout that is eating caddis needs to move quickly.
You may see one slashing at an egg layer or even rocketing out of the water after an escaping emerger
But of course, caddis are not the only speedsters in a trout stream.
Isonychia nymphs, damselfly nymphs, minnows ....

That's what the slashing and jumping is all about.