[Preamble:] I live in Ontario Canada (zone 4A); where we had a relatively easy winter. My main goals with beekeeping are to provide pollination to my fruit crops; and to help a struggling species. I live in a wonderful, natural area…mainly forest and meadow…450 acres with county forest on all sides. In other words; no regular farm ‘crops’ (corn, wheat, soybean) grown anywhere near my bees.
I treated my 3 hives for varroa spring and summer last year 2020 (they were: 1 over-wintered and 2 new nucs the year before, but treated them in fall of 2019). They were: 1 super strong, 1 really strong and 1 perhaps weaker; in the fall (2020) and I had suppered them but left honey supers on, so they had extra nutrition for the winter. [I have used this method in the past with great success.]
Upon spring examination I find the 3 almost identical: no live bees, no predation (mouse guards in place and secure, bear and raccoon protection in place and operational), no evidence of nosema, nor varroa (on bottom boards, with just ‘reading glasses’?).
The hives are absolutely packed with honey, lots of pollen stored. No 'up-ended" bee bodies, no evidence of a cluster in any of them!! No brood, but I wouldn’t expect that yet…
The very oddest thing of all was: as I was putting the hives back together (about an hour into my inspection), along comes a bee, from the forest! Another appears, then another…after 5 minutes more there are 5 bees surrounding the hives, 3 Honeybees, 1 dark larger bee and a (perhaps) mason bee.
Did my bees abscond into the forest?? All THREE hives? Am I THAT terrible a beekeeper?
Are the scouts returning for resources?
Any insight would be welcome…
Thanks!
KathysBees
Hi Kathy! Sorry to hear this news - I don’t know how much help I can be with speculation, but thought I’d at least welcome you to the forum 
I guess it’s possible, since you saw nobody at home…but all three of them, wow, it does seem extreme unless you can discover some compelling reason - other than how amazing the forest sounds compared to our flimsy langstroth shacks of course 
I sincerely doubt this! You described a pretty straightforward pattern of management and a high level of care and concern as a beekeeper. I’d just caution that you might not see as many mites with the naked, or even bespectacled eye, as could have been there.
Quite possibly, the little scoundrels! Or those bees could be from other feral forest hives. The scent of honey does carry and will attract all manner of potential takers, as you saw.
How many dead bees? Piles or just a few? Do you have any pictures you can share?
Hello and welcome to the Flow forum! 
Highly unlikely. I know you say that you treated, but honestly Varroa is the commonest cause of hive loss over winter. How did you treat? What were the post-treatment mite counts? Did you do a proper count using a sugar roll or alcohol wash? Sometimes it is hard to get the counts down in the fall with just one treatment. Depending on what you used, you may have encountered resistance, or just high numbers that needed more treatment. So Varroa would be top of my list. This article tells you what to look for in the hive, to see if that is a likely reason in your case:
https://beeinformed.org/2016/03/08/why-did-my-honey-bees-die/
Second most common is starvation, but you say there is plenty of honey left, so it isn’t that. Third would be cold combined with condensation. Did you insulate the hives, or have moisture quilts in place? Having said that, I would expect to see a large pile of bees in the bottom of the hive if this was the cause. So I am back to pointing my finger at Varroa… I am a bit of a broken record sometimes! 
Hi Dawn,
I am wondering if I should have treated again later fall too.
I treated with formic acid, both spring and fall. Last fall I wanted to get to it earlier so I did it mid September. I didn’t do the alcohol or sugar roll, either. I use the ‘sticky board’ test.
In 24 hours the hives had 0, 3, 1 mites and in 48 hours had 8, 13, 18. So I took that to mean the treatment worked quite well.
How long does it take to build resistance to the formic acid? I have always used it. Two hives were new nucs last spring and one was in its third year at my farm.
I wasn’t aware mites would make the bees just leave! This is only my 4th year caring for bees. Apparently the learning curve is rather steep!
The only insulation I use is a wrap of tar paper. The hives are situated on the south side of a thick Norway spruce windbreak. There was no moisture accumulation anywhere in them.
I will examine the link you sent. Thank you!
Hi Kathy, thank you for your thoughtful reply.
Resistance does not appear to be a problem with formic acid or oxalic acid. They are not insecticides/pharmaceuticals but instead work by a chemical reaction which usually hurts mites more than bees. You may know however that formic acid carries about a 10% risk of queen loss with each treatment, so that may be part of the issue.
I know that many people accept sticky board counts, but they are hugely inaccurate. I would rather do a sugar roll, alcohol wash or even an “accelerated mite drop” count if you have the equipment to vaporize oxalic acid. I completely understand your confusion, the information out there is quite misleading. Even if I think I have done a good treatment, I do another count a month after the end of the previous treatment course, and then treat again if needed. In my experience, Varroa has become much harder to control in the last 2 or 3 years, and repeated treatments seem to be almost compulsory, even if you have hygienic bees. 
It doesn’t quite work that way, but that is certainly how it appears if you look at the hive. Let me explain. I have 2 hives on a large paved area - no forest floor. When the mites get out of control, I start to see a lot of “crawlers” on the paving. There can be hundreds of them if you trust your bees to be hygienic and don’t treat (guilty! ) These bees are heavily infested with Varroa, and are newly emerged bees, which get thrown out of the hive because the workers notice that they are sick. Most of them are sick with DWV (deformed wing virus), even if they don’t have deformed wings. They die within a day or two, once outside the hive, and quickly disappear into the landscape. However, now the hive has lost a whole cohort of workers. If this happens day after day, by early winter, the hive has almost no workers left, and can’t make it through the winter. So they don’t abscond, they just shuffle away (too sick to fly) and contribute to the soil, not to the hive.
I think you are doing fine. You are asking questions and willing to learn. That is the way to get even better.
Please ask more if we can help again.
Thank you so much for your time and information.
That link you sent was really good also! Not exactly what I have, but very close.
I am going to get the container and start using the sugar roll method.
I am only 100% certain of one hive being queen right heading into last fall; so I possibly killed the other two with the formic acid. 
I am going to research other varroa treatments also.
And, although it makes no sense, financially; I am going to try again with a couple nucs. I hate giving up!
Hopefully your hives are thriving this spring!
Kathy
Mine are doing great thank you, after using Randy Oliver’s oxalic acid sponge method for Varroa control. It isn’t totally legal yet everywhere, but it is totally safe. The US EPA is working with him on getting it properly approved - shouldn’t be too long now. So your choice, but if you are willing to try it, you may be able to cross Varroa off your list of culprits:
We have one weak hive with a queen that has never laid well, but they made it through the winter and are building up now. We will probably boost her with a package and a queen replacement. Such is the role of a livestock manager - keep monitoring and do what you have to do for low performance…
I don’t have a hive, but I have been adopted by the many bees that visit my bird bath each day. I don’t know of any local beekeepers, and these visiting bees are probably nesting somewhere in local woodlands here in the hills east of Melbourne, Victoria, Australia. I noticed bee numbers were way down last year, but this year’s numbers have been great. I am popping in here on the subject of larvae deaths. Our weather sometimes brings cold snaps, and I fear many of the developing larvae succumb to the cold. I understand the bees then have the sad task of removing the dead larvae from the hive (or nest). Last week, I just happened to be lucky enough to capture a photo of a bee carrying one of those casualties. Just wanted to share my pic with you.
Beautiful pic, but I don’t see a larva. They are usually almost entirely white, sometimes with some color in the eyes. I am not a professional entomologist, but if anything that looks like part of the leg of a larger insect, either a queen or a bumblebee.
Yes I agree, I was able to zoom in on it & came up with the same conclusion. That being the case, it would be extremely rare to photograph something like that, I would think. One for Nat Geo.
Thanks for your comments. To my (non-expert) eyes, I thought I could see some little legs, and what I thought might me the beginnings of a fur coat. Could this possibly be a youngster somewhere between the white larval and ready-to-fly stages?
Hi Brian, amazing photo! It looks more like the leg of something larger to me as well though - have a look at this pic of pre-emergent bees:
Thanks, Eva. If it were a leg, I cannot imagine what the owner could be. We don’t have bumblebees here, and there are not too many dead queens around. Sounds like a job for Forensics!
Hey gang,
Nice to connect with cool bee people!
I have learned a lot here and hopefully more in the future!
(Newbee, here; so hopefully I can contribute at some point…)
Looking for experiences with oxailic acid with your bees; and if anyone from Canada has accessed it??
Thank you 
KathysBees
(705) 725-4059
Time to ping @Doug1 …
How about a cricket, or a cockroach?
Hi Eva, definitely not a cockroach, I’m an expert on them. If it is a queen’s leg, it would go to show how ruthless bees can be when it comes to killing them. Also, how rare would that photo be?
Thanks for all your suggestions. My own logic and observation can be summed up thus:
- What is the insect most likely for a bee to need to expel from the nest? I reckon that is probably an immature deceased bee.
- The subject seems to have the general morphology of an immature bee. It appears to have legs, and careful study of the picture suggests the existence of body hair.
- I have also spotted that the subject has faint (but perceptible) bee-like stripes.
However, I recognise that there are many other possibilities. I really think my bee’s payload will not be determined with sufficient certainty without input from an expert. Accordingly, I have sent my picture to an experienced entomologist, and I will look forward to whatever advice I am offered.
I will, of course, report whatever expert advice I receive.
Take it from us, it’s not an immature deceased bee. Between the 3 of us, as well as my mentor, there’s probably a century’s worth of beekeeping experience. But… we could be wrong.