Invert's Huddle?

[Gujustud]

Is it normal for the inverts of the tank to sit around and have a midnight huddle?

I just came back from downtown, about 12:30am, and thought I'd take a peek at my tank. Only lights in the room is a small blue bulb, and some of the street lighting (tank lighting turned off already).

I was able to count 3 hermit crabs, and 5 snails all huddled together (and on top of each other) on the top of one rock. It was the most interesting thing I've seen.

To make things more interesting, I noticed something flying around in my tank (and as I have no fish in there, I found this odd), so I turned on the hallway lighting to give the room more light, and found my peppermint shrimp flying around the tank, up on the walls and everything. VERY VERY weird... never seen anything like it before?

Or is this a little secret that newbs like me have no idea about?