Dad and myself were reloading some 243 ammo tonight and he could not fill one case, the powder kept over flowing and when he tried to dump the powder out alot of it would stick inside, when I looked inside the case I could see some powder suspended right in the middle of the case and upon closer examination it looked like the powder was stuck in a spider web. Sure enough when I poked it out with a pick it was a silky white spider web. In over 20 years of reloading I have never seen this before. The cases were cleaned and sized and primed less than a month ago. Very strange.

Well then I assume you stored them in an opened container. I've had cases primed and ready to load for months but always in a container with a tight fitting lid.

Exactly, if they were primed and ready to load like the OP stated!

That's a new one on me.

Bronko22000 you are correct I did not have them in a sealed container but who would have thought a tiny spider would get inside a small necked case and spin a web?

should have chambered it in your rifle and touched it off with just the primer. would have really blowed that spiders mind. just kidding.

It doesn't really matter that the spider did that because that is only one thing that happened. You should also keep them in a closed container to eliminate the possibility of moisture contaminating the primer while the case is open, rather than covered at all times after priming.