Worms wont usually leave a food source, so something else is most likely the culprit here. Posting photos here could help your problem be diagnosed.

Yes, you'd notice if they escaped. Dead worms decompose in a bin super fast, so you may not find bodies even with large die-offs.

How many worms were in there at the start? What kind of bedding are you using? Has it been too dry or too moist? Any chance the area got very hot or cold? What kind of food were you feeding? What kind of bin is it?

Yes, you won't find any worm corpses in a worm bin, the worms are mostly water to begin with... have you ever seen one that escaped and then found dried up on the floor? Not much left is there, however inside a worm bin is basically a compost pile filled with things that's only purpose is to break down dead matter... thus no worm corpses.

How many worms did you have to start and how big is the bin? How much of what were you feeding them? Describe exactly how you went about looking for the live worms left in the bin when you counted only five?

We have a 1.5x2' Rubbermaid with air holes (I think there's good air ventilation now, although in the beginning a bit of condensation collected in the lower part of the bin, which prompted me to drill more holes). Definitely not too cold but maybe it got too warm?? Our apartment does get up to 75 degrees on hot days (south-facing windows) but they're in a cool, dark cabinet. The bedding is soil and moistened, shredded, plain newsprint paper, plus the occasional toilet paper roll, coffee filter, dried crushed eggshell, etc. I feed out every other day and learned quickly not to feed when they hadn't eaten what was there, and lately there hasn't been much leftover food but I only feed maybe 6 oz. of food a day (mostly pear and lettuce cores and coffee grounds at this point). I keep the bin moist but not wet, I spray the bedding maybe once a week with a light mist and spritz the soil too if it feels a little dry. I noticed some mites for a couple weeks but as far as I could tell they weren't the predatory variety, although maybe they were? Their numbers have decreased too...so I guess if they were killing the worms and/or scavenging the dead ones, they're running out of food too. One pot worm once but no other critters I can see.

I started checking for the worms every couple days after the first two weeks by gently turning the bedding and the soil that's settled at the bottom - it's not a large bin so it's really not difficult to hunt through. Their numbers already seemed depleted after a couple weeks. No worm bodies at all, but I guess if they decompose so quickly I wouldn't see them...but then wouldn't the bin smell? We started with what was advertised as a pound of worms, although there was NO way it was 1000 worms as I've read - maybe a couple hundred. And now there are five, and one doesn't look so hot - pale and lethargic.

I hope that's helpful, and I appreciate the feedback! I guess now that I read my own responses it might have been temperature/inadequate airflow in that first week, or they're being killed by mites, and they decomposed too fast for me to see the die-off...if it's one of those, which would be more probable? I don't have the budget to keep purchasing worms, those little dudes are expensive.

I don't see any obvious issues in what you're saying about your setup. A little condensation forming inside is par for the course, and if the airflow was really inadequate enough to kill your worms, the food you put in would be decomposing with a garbagey smell as well.

That's a small bin for 1000 worms, but then you said you weren't so sure you really got 1000 at the outset. I assume you got red wigglers? Where did you buy them from? Reputable source? Local or mail order? How did they look when you first got them? It doesn't sound like they ever really thrived.

Soil's not necessary in a bin, but on the other hand, it shouldn't normally cause a problem either. Where did the soil come from?

You hear about these alleged "predatory mites", but I've never seen them or heard an actual firsthand account of them. I don't think they are particularly common but I suppose they can't be ruled out. It's just that practically all bins have mites in them and almost without exception they're the harmless kind.

Okay so here are my thoughts based upon what you've written...

I don't think high bin/bedding temperature would have killed them unless it got into the mid-to-upper-80's (even then it would have had to permeated the entire bin and would have had to stay at those temps for more than 12 hours... no I don't think bin temperature would have killed them). I'm confused as to just how much soil was in the bin... more than a handful is never necessary... you must remember these are composting worms and are not built strong enough to dig through actual real soil... also I assume that the soil was how the mites were introduced into the bin. And speaking of mites, though there is supposed to be one type of mite that can attack worms, I seriously doubt those are the mites you have in your bin. Wetness and lack of air flow are also not big worm killers... I routinely pull live, healthy worms out of my koi pond and filters... and lots of people have plastic worm bins with no more than a few 1/4" holes drilled into the top for air-gas exchange.

I'm perplexed by how you can feed just 5 worms or even five dozen worms 6oz of food a day (at this point I'll assume 6 fl oz but even if its 6weight oz that's still quite a lot as that is more than 2.6 lbs per week) and have it not pile up to dangerous levels (in terms of by-products that ~ 4 cu-ft of compost bin that's matured and full of composting creatures can't even keep up with). Add to this, you've only had them for a month... I know from personal experience that to build a worm bin up from scratch takes a lot longer than that to get it to a matured state where the worms are finally able to live up to their reputation of eating half their weight per day... twelve dozen worms (that's 144) won't even weigh in at 1 ounce, you'd feed them 6 ounces per WEEK.

So here are my guesses as to what's happened...

Either you're miscounting the number of worms survivors... This is quite possible since worms can, especially under stress, ball up in a mass... and unless you happen to dig in the exact right spot may miss seeing that greater population mass, which would NOT have grown any larger in only a month... 1000 reds tightly balled up is like the size of tennis ball). The other possibility (its what I'm thinking may have actually happened) is that unintentional overfeeding lead to either an ammonia (protein) or alcohol (sugar) build-up temporarily because the bin is so new and the proper bacteria populations (and other bin micro-creatures) have not had time to multiple-up and balance out and so many of the worms could not avoid those toxic conditions because your bin is so small (especially so if you spread the feedings around the bin). This scenario would not be extraordinary at all... its something most of us experience first hand during the initial stages of starting a fresh bin from scratch.

If that is what's happened its not all bad news.... your bin is a month closer to maturity (which likely will take 2-3 months to reach maturity) you have gained experience over the first month and should be able to keep the survivors (the hardiest) going and now gradually multiple the numbers back up over the course of the summer months. Good luck there. I'll be interested in seeing what some of the others on the forum here think happened.

That's all great information! I should note I'm really horrible at estimating weight and volume, but I did stop feeding until the existing food was mostly gone...although I didn't learn that for a couple weeks, so your theory sounds very plausible. There's about an inch of soil on the bottom of the bin right now (well, soil and coffee grounds, since I only started with a couple handfuls of soil), and it's only IN the soil that I can find worms...and I am almost positive that there are none. I mean, I sifted through that entire thing (although I didn't know so many worms could fit in such a small volume!) and found literally nothing except a few unhappy worms. I honestly don't think there's hiding anywhere, so I feel like I'll need to buy new worms...I'll let it rest for a bit though and see what happens, and in the meantime, is there a way I can re-balance the pH or chemical makeup of the bin? Or will it suffice to just stop adding food for a while?

Thanks again!!!

Yes, stop adding food for awhile... until most of what's in there disappears anyway. When you do begin to fed again try to keep it roughly alternating between just two locations only. I don't know how deep you've got the bedding currently but try for at least 6-8 inches... so if you did add too much food you can help dilute with more bedding. Add more organic matter for bedding (it also will double as a food source)... stuff like shredded paper products (news print and cardboard) also coco coir is really great because its fluffy and retains moisture and air flow (movement) and is near neutral pH. If you choose to add peat instead then you'll have to compensate for the acidity by adding some lime... in any case do keep adding eggshells as the worms need the calcium and it will help buffer the bin pH.

Judging from all you've written, I'm betting you've not lost as many worms as you believe you have. Just give it time and everything will right itself. Good luck.