addendum 1: the base pan where liquid collects smells like a pig farm. If you have ever been downwind of a pig farm, you will understand what I mean.

I agree with klem1: very happy & healthy BSF larvea.

The soil is very wet, and I have added no water. What's happening with my Ex-worms? Sounds like too much feeding, not enough shredded newspaper and your ex-worms are part of that foul smelly liquid now. They might have left cocoons in there that might hatch and live if the bin condition gets corrected.

How do I treat the newcomers? BT spray? I wouldn't use BT spray. Before you add newcomers, I would fix the bin condition if it is still smelly and wet. Tilt 1 end by putting a piece of wood of ca 1.5 or 2 inches to force liquid to pool faster to the other end, where you put an empty tin can (remove the other end so it's a see through) in one corner. A big enough can so you can put your hand through. Put an old t-shirt or any rag loosly in the see though can to absorb the collecting liquid that you will wring dry from time to time. Suggestion: use gloves because if the bins is still stincky, the smell will stick to your skin for some time even after vigorous washing.

To speed up the process, line the walls (move the contents aside so you can jam the cardboard to the bottom) with several layers of corrugated cardboard, with ribs vertically to help evaporation. You can leave these in place (or replace with dry ones when too wet, re-use them after dried out). Worms like to hide out in the "ribs", a good place to rub off their cocoons and a good supply of microbes available. I line all my bins with corrugated CB and have to be careful when shredding them by hand because of the many (fat) worms living there. It's good practice to replace the CCB with new ones so the worms can be removed and get them to mate and make more cocoons.

I would also fluff the contents from time to time (like once every day or 2) so it's not a massive solid clump, free trapped bad gasses in it. You might want to add rolled up CCB through out, like chimneys, sort of. Add a layer of dry shredded newspaper atop the exposed mass. It's OK when some of this get mixed when fluffing for now but not after you added newcomers. You should be ready to add newcomers once there's NO SMELL and not too wet. I would add the worms to 1 place and let them scatter at will. Add food sparingly, next to where you put the worms. I usually feed in 1 spot so it's easy to remove if I notice something went wrong, rather than surface feeding throughout.

I would do all that because I have the space for an extra bin and thinking of the possible cocoons left. Anything to save a worm, right?

Good luck and keep us posted.

PS: Do you cover your bin? If yes, how/what with?

Good advice above. More simple advice: it's easy to overfeed, and you basically can't have too much bedding. Too wet is worse than a bit too dry (as long as not bonedry), so add dry bedding if in doubt.

Thanks to you all. I cover the tub with the cap that comes with the Rubbermaid 20-gal. tote. I left it off for a few days, stirred it with a garden fork and I saw a few worms, and much fewer larvae. I don't think they care for the fresh drier air. I think over-feeding might have been the culprit--the worms had started to migrate into the upper tub, but not wholesale. The food I added to the top tub likely overpowered the new arrivals. I will leave it to dry out a few more days and see if they re-populate. From 10 thousand to a handful was startling. Thanks again.

also, the "newcomers" I referred to were the fly larvae. I think the air-out may solve the problem. I'll hold off on the Bt.

more browns!

Here's what I did with the lid. I cut out most of it, leaving about 1.5" material. Then I glued weed cloth/weed barrier in it's place. That will minimize the flies, fruit flies, BSFs infestation.

Lately I saw different kind of weed cloth sold. Don't get the plastic with the tiny tiny holes. I got the one that feels like cloth.

This sounds doable. Thanks.

I have found a thick layer of dry shredded paper (a couple of inches at least, more if you can, three-four is better) on the top to be pretty effective at keeping flies and others out, and it also tends to regulate moisture a bit within the bin (it absorbs some water), lets air get down below, absorbs odours to some degree (which may make less attractive to flies and other unwanted denizens), and is convenient for feeding (pull the shredded paper aside, put your food in, put the paper back). It also serves as a brown in the bin, as over time it will get damp and break down and get incorporated in the stuff below (more will need to be added from time to time). Seems to also provide a 'safe place' for worms to hang out in if they don't like conditions below, while reducing their wandering (they don't commute through the drier paper on top with no food). You can combine this approach with a lid with a screen; you may find no lid needed at all.

Twice now I've heard reference to "brown"--can you explain?

Sorry, my mistake - in vermicomposting, generally refer to bedding and not browns (as in regular composting). Not exactly the same but similar. Cardboard and paper most common bedding for worms, both considered browns in composting.

I'd probably throw it away and start over.

The soldier fly larvae showing up in your bin indicates that you have overfed. They will eat up the food, and under the right circumstances, the worms will live at the edges and wait until the BSFL are done, and then come in after.

However, these conditions (way too much food, way too many BSFL) are what worms hate, and they'll die if they simply can't move away from the action.

See if you can find any worms in the bin at all. Pull them out and put them in a smaller bin for a while. I did this once, and after removing some worms, just buried whatever else was in the pile in dirt to kill the smell.

Feed smaller amounts until your worm population grows. Recognize that the BSFL are indicators. A few are not much of a problem, but many shows you're over feeding.