But why does it have an anal claw?

Today was an amazing day, we all learned so much, and had fun doing it, whether it was electrofishing, water and soil sampling, floating the river, lectures on geographical and ecological histories of the area and river, the experience was great. There were several things I saw, did, and learned that left impressions. It's hard to narrow it down to just one thing to blog about, without writing a novel; but to pick one of those things, perhaps being the juvenile minded person I am, occured after our group finished collecting electrofied fish and started scraping up creatures from the mucky river floor and placing them in a tub to be identified. As we were looking at the different types of creatures, their attributes, and how to identify them, I noticed that one creature called a Caddisfly, had a few very interesting features, one of which is that it lives in a protective shell casing that it made itself, and the other is that it has an anal claw. What the heck is an anal claw, and what is it used for, I asked? "To grab onto rocks someone said", another suggested that it might be for "mating purposes?" I was thinking that maybe it had something to do with that mobile home on it's back? As it turns out, I was right, The young Caddisfly actually uses its anal claw to grip onto its shell. Cool huh?