Christmas Carol

I've been looking forward to this. This is the one day between October and March that I get the chance to see bees and post a picture of them. The rest of the time the hive stays closed so that they can best maintain their body temperature. There are drops of liquid on top of the frames, and even a few on the bees. They are the reason for this intrusion into their seclusion. We have just finished trickling 5ml of the fluid into each seam between two frames, directly on to the bees snuggling there

The liquid is a solution of sugar (1 part sugar to 1.25 parts water, by weight - about half of the maximum sugar you could dissolve) with some crystals of Oxalic acid dissolved in it, to create a 3.2% weight/volume solution of acid (for comparison, vinegar is 5-8% acetic acid - a similar organic acid). Oxalic acid gets its name from Oxalis - wood sorrel - which tastes acidic if you bite the leaves. It's also found naturally in brassicas, spinach, quinoa and, notoriously, rhubarb leaves. You need to eat a lot of rhubarb leaves to do you harm, but apparently this did happen a few times during WWI, when they were recommend as a food source

The purpose of this kitchen chemistry, and showering the unsuspecting bees, is to cause the parasitic Varroa mites that are clinging to the bees to release their hold and fall through the mesh floor of the hive to their doom. Varroa have a particular dislike of organic acids, and trickling with this solution, fumigating the hive with oxalic acid vapour, or inserting strips into a hive that slow-release formic acid are all used as methods of mite control. We apply the treatment at this moment in the year because we are hoping that there will be very few new young bees growing in cells right now. The Varroa reproduce in those cells where the young bees are growing, and the wax caps that seal them in prevent the acid reaching them, so they remain in the hive to rebuild the population much more rapidly

As an aside, note that the bees are all congregated in one part of the hive. This is the famous 'winter cluster of the bees' - their reaction to cold weather by clustering to reduce their rate of heat loss