Is that ball of worms all that is left? If so pick them up and put them in a different bed with much drier materials. If you have fed to much then the bed is probably going sour also. Put the materials from the original bed in a bucket and let it dry out and watch for more worms hatching out. fluff it up and add some dry newspaper to help get it drier.

Thanks for your advice wfike! There are actually plenty of other worms in the rest of the bin. That's the weird thing. The worms don't seem to be sick or dying. They're super wriggly and very happy seeming (if a worm can seem happy). Even some of the worms in the ball will start to crawl underneath when the light reaches them. And the bed honestly isn't very damp at all. Doesn't smell, etc. I just can't figure out why some of the darn worms are all clumped up. Worm orgy? Has anyone else ever seen this happen?

I have seen them do this when there was loud noise or a vibration of some kind. When you do the cone method of harvesting worms they wind up balled up at the bottom of the cone. You got the bin on top of something that is vibrating? Refrigerator or something?

I don't know if I would call it all balled up but I usually find huge numbers of worms in the corners of the bin. They seem to just like the conditions there though there are plenty of worms throughout the rest of the bin.

Here is a link that might be useful: My bin

Try measuring the temp of the bedding! (grocery store will sell a meat thermometer for about 5 dollars. they work great!) I've had worms crawl to the top and ball up and or crawl to edges when the bedding heats... Somewhere around 80F to 85F. If the bedding is warming I just usually leave it alone,

Fluffing it to cool it off DOESN'T WORK! It will just introduce more oxygen into the mix causing the bacteria to heat the bin more!

I will sometimes mix up bedding and a few food scraps a week before I add it to the bin to let it age a bit. Two to three days after the worms get to it, It starts to warm a bit. If I notice that the worms are fleeing the stuff, I take a newspaper still folded and get it damp and put it on the side of bin or on top so that the worms have something cooler and damp to escape into if the warmth gets too much for them.

During this whole process I will usually have plenty of other worms that aren't deterred by the warmth in the least and will happily hang out in the warmer parts.

Hope that helps!