The probable answer, based on all the responses, for the larva question is what is in front of the mouth is the casing, with the larva beginning, being behind the fish. I think the casing got stuck to the beak of the dipper. He either ended up shaking it off or gave it to one of his kids. I agree with Amy on the needles; the plastic looking material could have been the excreations the caddisfly uses to build the casing. And it was all wet, so the reflection.

Every time a dipper gets an encased caddisfly larva, he is out of the river and on a rock, sometimes dropping them to get the head, shaking them several times to throw off the casing. If that does not work he slaps it on the rock. They rinse off the larva after releasing it from its confinemeant.
I have posted a picture of the only other time I have seen excess debris in their mouth, looks like a leaf stem, plus the best look at the casing.

http://e-picturebookdesigners.com/debris.htm

By the time I wake, the little ones could be wandering the river. The mother is ready, she is standing outside the nest, on a log, beckoning her babies. Sometimes going to the nest, without food; tempting them to follow her.

Please, give me some sunshine when they fledge.

Don Wallace
Sequim
don at e-picturebookdesigners.com