What Are Those Ants DOING?

I'll be honest.  The ants have been a bit boring lately. At first they were SO fun to watch, as they vigorously tunneled through their blue goo to make tunnels.

Then we had the Great Ant Escape (see earlier post).  That was not fun, but it was exciting.

But since then, they've settled into a less exciting routine. They scurry through existing tunnels. They eat, presumably. They die. (Yes, many are dead. That is normal as they don't have a long life span.)

A few days ago, I went in to check on them and found...a ball.

 You can see it on the right side of the ant farm.

 It is HUGE, compared to an ant.  It definitely wasn't there before, so they made it!

I admit to being perplexed, bemused, and amazed! 

There must be a purpose for it, but what is it?

Joseph pointed out that it blocked off the exit (or entrance) to a couple of tunnels.  Maybe they made the ball for that purpose, to block off a tunnel?

 Anyway, it is interesting.

  (Here is a larger picture of it.  You can see the tunnels below it that are blocked off now.)