The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
The clumsy-looking mayfly nymphs of the genus Baetisca are surprisingly good swimmers.
Water boatmen are excellent swimmers, and you can see here how they use their oars to push themselves through the water, a motion easily imitated by the fly fisher.
Damselfly nymphs are among the most effective invertebrate predators in freshwater. You have to see one in motion to get a feel for their slow, deliberate style of stalking.