This weekend in North Texas the temperatures dropped to -11C, but with typical Texas weather, the temperature this afternoon was close to 20C. When I went out this afternoon to check my hive, I noticed quickly that there were no bees doing any bio flights. There was some activity prior to this weekend. I thought I should at least glance through the opening in the inner cover to see if I saw any activity. There were no bees moving, so I removed the inner cover only to see nothing but dead bees. It appears that the bees froze. The reason the bees could have froze is because the colony seemed to be very small. If I put the dead bees in a container, they would have probably barely filled a half liter container, definitely not a liter worth of bees. I’m guessing the small number of bees would not have been able to keep warm enough to survive the cold temps. One of my many unknowns is why the colony had become so small. The bees had left behind a lot of stores - 4 full frames of honey and some amount of honey & pollen on the remaining 12 frames (2 fully drawn 8 frame Langs). This was a new colony started from a 3 frame NUC in April '16, so they did a great job building up the hive. I did see the first mites on the corflut slider in late October - I’m guessing this has something to do with the smaller colony size this winter. I have attached a couple pictures. I will have lots of frames with honey and pollen to get a new colony or two started next spring. Any guesses on what could have caused the colony collapse would be greatly appreciated - would like to improve my chances next year.
Varroa maybe??? Did you treat this hive this fall?
John - Thank you for the reply; I did not treat. I never saw any indications of Varroa until the end of October. I check the outside of the hive and corflute almost daily. The colony also always had very low % of drone brood on foundationless frames. I also wonder if I could have lost the queen at some point, but thought there would be queen cells or drone layers. My last full inspection was early October and there were lots of healthy looking bees & lots of stores, no visual issues with the comb. I could have missed something though ( I must have)! Thank you.
Tim,
I treated my hives in August n was thinking I
was good … wrong ! Mentor encourage me to slide a white sheet of paper mid December n check … Since we had such a long mild autumn the bees got reinfected. I
was able to treat with Oxide vapor (temp was still okay). Saved two hives but the third had higher number of mites on the paper ( over 30 ct in 24 hour check ! So lost it.
Your right … You could have lost the Queen … Any chance you saw her dead body when you checked ? But I’m guessing it was mites not weather or queen loss … Sorry ! Im learning with you ! It’s a tough learning curve ! 
. Oh ! I had to get out my new Celisus to F converter … Not use to seeing that measurement out of Texas 
u
Good luck n keep at it bro !
Gerald
More likely you had a failed/lost queen and the colony just dwindled away.
I don’t see signs of varroa on that frame. Are there any frames with old brood on that you can show us?
By the way, natural mite drop is not an accurate indication of mite numbers
You have had some great responses already. Both @Dee and @Gerald_Nickel bring up some prime suspects. I agree with them that either varroa or loss of the queen are the most likely culprits. In fact, varroa is probably the most common cause of colony loss over winter, the others are starvation and condensation (wet, cold bees die very fast). If you want to do a further “post-mortem” inspection of your hive, you could look for crystals made by varroa on the upper walls of brood cells. There is a very nice photo of that at www.beeinformed.org:
If you see a lot of that in the brood cells, it was probably varroa that killed them. Actually, I would encourage you to read the whole article. It is very well-written:
https://beeinformed.org/2016/03/08/why-did-my-honey-bees-die/
I would strongly suggest you do a sugar roll test for varroa next year in the late summer. It is much more accurate than counting mites on the bottom board. I have VSH bees, and one of my hives needed treating this year despite the hygienic bees. I wouldn’t have known without testing the bees, well, except that I could see DWV signs in some bees. That treated colony is doing well now, otherwise I could have lost them. I know that people don’t like to treat, but as a hobby beekeeper, I would prefer to treat and save the hive. I don’t have enough hives to rescue the situation if I lose them to varroa, whereas commercial and larger scale beekeepers can easily recover from 50% losses.
Thank you for the feedback @Gerald_Nickel. I did not see the Queen, but may take another look. I will try again in the Spring! Based on the article that @Dawn_SD linked in her response, the colony was probably a victim of Varroa.
Thank you for the reply @Dee. I will take pictures of the primary brood frames, but don’t remember seeing any actual brood - that’s the reason I think I could have lost the queen. Mites were an issue in late October/early November though, I did see the first mites on the corflute and saw a couple bees with DWV.
Thank you @Dawn_SD for the link to the article - sounds very familiar to my colony. I’ll take a closer look at the brood frames to see if there are any signs of Varroa.
Yes what Dawn has shown you is varroa faeces. A lot of people mistake it for crystallised honey remnants
We are finally getting our own British Bred Hygienic bees (well sort of,from LASI) and their research shows that having hygienic bees doesn’t preclude them having to be treated it simply extends the interval between treatments
Tim, Dee, Dawn,
Great discussion here. Really learn n enjoy such productive thoughts n discourse on the forum most of the time. This one was very valuable to me.
If n when I’m 100% sure mine are 100% history I will try to add pix n data. I did loss Pine n Cedar hives to the mites …verified those finding back in September/October. Currently it’s way too chilly (below 35 dgs F) here in Puget Sound foothills SE of Seattle. I’m basing my loss by smaller n smaller n now no infra-red indicator last photo session n high amount of more dead bees on SBB screen n unable to hear a noticeable buzz inside when I tap the hive. It maybe that the cluster is WAY too small to be seen on camera or heard. I have my other two healthy colonies to compare n thus my assumption it’s totally gone. When we get warmer day I’ll at least pop open n peer in under the crown board n see if any bees working the winter patties still. It’s been in the teens n 20’s so not chancing the inspection !!!
Again, thanks for the great input n thots. It’s a learning curve almost seeking even during the winter.
Ta Ta you guys,
This graph is the from the monitor inside my Flow-hive … Other infra-pix is Maple n smaller Alder hive (a double deep Nuc) next to it.
I would say that is a realistic expectation. I think some colonies will not need treating. However, it can’t be assumed that they will survive without treatment just because they are VSH. You still have to check, and mostly you won’t need to treat, but sometimes you will, unless you have spare hives to repopulate. Nothing is perfect, even Darwin had losses… 
Good luck @Gerald_Nickel, doesn’t look too promising on your big hive with such a small heat image - you have a lot more technology than me, very helpful! Here is a picture of one of the original brood frames (one of the three that were part of the nuc). There are a few cells on both sides of the frame where the bees did not fully develop and leave the cell. The upper left hand corner is where the small colony huddled (upper south side of hive). There are a few pollen cells below the bees. On the right hand side of the frame is honey up top and un-capped honey on the lower right side. One other frame had similar few un-developed brood cells, but there was no other live or active brood throughout the hive. 
I haven’t enlarged this frame like I did the other you posted but you can see perforated brood cappings. Together with the varroa faeces it’s diagnostic. It’s areal bummer…so sorry!
Gerald,
Try taking a picture from underneath. Your thermal camera should pick up each seam of bees
Thank you for the diagnosis @Dee - at least I have a good understanding of what caused the collapse. I hoped to be treatment free, but hope will probably not be a good strategy with the next colony. I did get 4 frames of honey from the hive and will have 9 or 10 frames of comb & partial honey / pollen to help kickstart the next 2 colonies. I’ll cycle out the old brood frames. Thank you again for the replies.
Deleted because of no reason.
I trade on the stock market. One of the sayings we have is that “Hopium” is dangerous stuff. As you now know, it applies to beekeeping too. Sorry for your loss.
Dee, I’ll try that angle ! Wasn’t thinking about pix access upward. I’ll have to see if I can get my brother back to my apiary with his camera. Hoping to have a personal infra camera someday … But as my mom often use to say, “If wishes were horses … Then beggars would ride” !
Today I cheated ! Couldn’t resist ! A picture of two is worth a thousand words ! 
. There were no bees at the winter patties so I lifted the nearest … Took my bright flashlight n peered down thru the center framed. SCORE ! Few bees working their way up n more below. It doesn’t look like a huge cluster. Probably baseball at best ( didn’t want to leave open as it was only in the upper 30’s then)… So there is life … Not sure big enough to make Spring but who knows. Whispering a prayer or two n crossing my fingers as well. Never take anything per granted !
The mites sure did trim this huge hive down ! It was so big n healthy early last autumn ! It’s sure different from the 1950’s n 60’s. Not sorry I got back into beekeeping. Just trying to get a handle on all this new mess n treatments or not. I’ve Choosen to treat mine.
Forward n onward ! What we got to loss. I
have four new Nucs ordered for Spring delivery. But still love to get that baseball sized Birch Hive thru n growing again !
Cheers,
Gerald.