Whenever there is a bad smell, I think anaerobic. If the material in that plastic bin is 10" deep, I would say it is time, (past time), to harvest. I would guess that there is not much air in that compacted bottom of your bin and with no air you get..bad smell. I have had bins do this and I did stir it up, left the top off and the smell dissipated pretty quickly. I then harvested and put the worms in new bedding. The smelly castings could be stirred up and put in a rubbermaid type tote, with air/drainage holes drilled, just like your bin. It can be stored a long time like this and will dry out and get better with age. (Just make sure your storage container is not airtight, as it is a living material.)

Waterfalls,

First, of all it's good to hear that the worms are still there and not making a mass exodus so that's a plus and it may not be too bad. We may need some more info to better help assess the bin condition.

It sounds like you've got anaerobic conditions in your bin. There are several reasons that this could be happening. It could be there aren't enough holes in the bin or the bottom holes may be clogged with bedding. You might want to put a pillow using landscape fabric and styrofoam peanuts in the bottom to keep the bottom holes clear (You might want to search the forum for Kelly's bin plan). Do you have some holes near the top of the bin also? You must have some holes for the spiders, beatles and slugs to come in. Is the bin on the ground or do you have it on some bricks so the bottom holes get air? I have my bins outside on a few bricks with alot of holes on the bottom and an on the bottom sides an inch from the bottom. On the sides I have them spaced about 3 inches apart. Most of the holes are 1/4 inch in diameter.

Of the 8-10 inches of bedding how much of the bottom layer is wet?

How many lbs of worms do you have in the bin and how much veggies are you feeding? The moisture could be from the veggies.

Is the bedding matted? If so it may be the bedding that is making keeping the air out. If you don't have enough bedding it could also be the culprit. You might want to mix in some dry shredded newspaper or a little shredded or cut up cardboard (my favorite, I don't know how much the worms care) and fluff it to dry it up a bit.

My bins are filled with bedding with only 3 to 4 inches from the top. I'm a rookie, but I haven't had moisture problems except for the very bottom inch being wet when I harvested.

If you don't think you have enough bedding in the bin or a low amount compared to the food you have move the existing wet bedding to one side and add some moist bedding the other side. It should be as moist as a wrong out sponge. Check it and don't feed the bin for a while. I usually check the oldest pocket to see if the food is gone before adding new food.

Hope this helps,
Charles