It can happen to any of us.
And this year, it will be happening to many of our colonies.
Here in the Pacific Northwest we had a very long, wet and cold spring that denied us early access to our overwintered colonies. By the time we could get into the hives, swarm season was in full swing. With only 8 weeks to go before the main honey flow (blackberry) this made spring treatment very hard if not impossible to do.
The June blackberry bloom was unusually late. The bees took a long time to complete capping, and most of us had to pull the honey supers with a lot more honey uncapped than usual. My refractometer got a good workout this year.
So mite treatments were critically delayed.
And then.
And then, we had a gloriously long, incredibly warm and sunny fall. Bees are still brooding, although the weather has finally turned chilly and rainy. It is October 25th!
Nice that the bees can build up so nicely for winter. Unfortunately, when bees build up = brood = make baby bees, mites build up too. And bees that go into winter with high mite loads are very likely to suddenly crash and die in the first November cold snaps.
Bad as that is, not all hives make it to November. Untreated colonies, particularly in a year like the one we’ve had, often crash from Varroasis in late summer.
Here is an excellent presentation on what that looks like.
Here We Bee 
Excellent video!
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There is a wave of opinion coming from the UK of beekeepers reducing treatment and keeping the colonies that survive with varroa i.e. hygienic colonies. This only works, I think, for amateur beekeepers with small colony numbers. Amelia
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That wave of treatment free beekeeping washed over North America as I began beekeeping 15 years ago. In spite of much effort, no one has been able to establish lines of meaningfully Varroa-proof bees. I pin my hopes on our ability to alter the mite genetics such that we can render them harmless: that research is under way.
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