Both the immature tenerals and the mature damsels are effective flies. They get blown into the water. They drown and are taken underwater as sunken damsels.

Damsels have an immature teneral phase and then they undergo a color change to the mature phase. After mating the females must deposit their eggs in the water. Like some caddis they even go underwater to deposit their eggs so they are available to the trout. Being large insects the trout seek then out and they even leap out of the water after low flying damsels.

http://www.youtube.com/watch?v=-GtZC...eature=related

http://www.youtube.com/watch?v=UGJMAGYTcpQ

http://www.youtube.com/watch?v=hLIGywbbNNk

The foam bodied or foam thorax patterns are less effective than the ones that can sink because you cannot imitate a drowned damsel with a foam bodied fly. I tie both the banded blue adult and the tan teneral phase.

http://www.garyborger.com/2010/01/20...d-butt-damsel/

Here's a version with a foam thorax.

http://www.mwflytying.com/patterns/damsel_fly_page.html

When I mentioned the patterns using foam to Gary, he asked me if I thought he hadn't thought of that. That's when he explained that trout love drowned damsels