I'm sorry I can't "picture" the problem other than the spiders. I can see why you'd want rid of them. Are these channels 2 inches deep x 2 inches wide? I've seen where contractors will place a sort of "keyway" that is formed into the concrete walls. The "key" is a strip of 2" stock that is dovetailed into the wall and are put in place before the concrete wall is poured. Their purpose is to have something to nail furing strips to when finishing basement walls. If the key has pulled out of the keyway it will leave a channel. My suggestion would be to rip 2x4s and try to fit them back into the channel. It will be hard to get a good fit because of the dovetail formed into the concrete. Other than that, I'm not sure why the channels are there. Maybe there for stringing electical wires before putting up paneling though this certainly isn't standard procedure.