By Jack Pritchard of Rose Hill & Iffley Low Carbon Group
The seasons are turning: we have days of fireworks and poppies, of squirrels skittish on ripe conkers, and clock-hours turning back. I worry about the bees. As I walk, misty-breathed beside the Thames, I think of them huddled together in the hive, with only thin pine walls to protect them from the turning of the year.The colony which inhabited this hive last autumn did not survive to see the spring: a combination of varroa-mites and frosty-days proved too much for them. My first solo beekeeping experience had been cleaning out the hive – removing kitchen-ladles-full of dead bees and placing them in a fire, to dispatch them to whichever airy heaven bees fly.
I did not want to repeat that experience, so decided to take every precaution to prepare the hive for the winter. I had not harvested any honey, to preserve as much energy in the hive as possible. And I had fed with sugar-water in mid-September, to further increase the levels of winter stores. But it still felt that the hive could get too cold – the sides were much thinner than the hollowed trees and stone-walls where the bees’ wild cousins would be settling for their winters.
Some years ago, I helped with an energy-efficiency project in Oxford. A small group of volunteers wandered the streets of Rose Hill, taking infra-red photographs of houses and advising homeowners on how best to keep the heat inside. The thermal-imaging camera transformed suburban streets into a psychedelic wonderland – leaky air-vents glowed lemon-yellow, radiators showed orange through thin walls, and poorly-insulated roofs glowed a bright magenta. I wondered if I could use the same technology to see if my hive was leaking heat, and to identify the best way to insulate it.
My hive has a metal-clad roof, which throws-off the readings a little. The camera effectively works by measuring the ‘light’ coming from a surface (although it’s light at a frequency which our eyes can’t see). When the camera is pointed at a mirrored surface it reads the temperature of the reflected image, rather than that of the surface itself. So to see the heat at the top of the hive, I had to remove the roof, and look at the tops of the bars. This shows where the heat is coming from, but doesn’t give any sense of the insulation that the roof provides.
First, I addressed the heat leaking from around the edges of the inspection board (the floor of the hive). Two lengths of pipe-lagging foam fitted neatly along the base of the hive, and narrow-nails meant that it could be popped on and off to provide access to the inspection board if needed. Although this solved most obvious source of heat-loss, the walls of the hive still glowed alarmingly on the camera-screen.
The most interesting observation was a knot of wood in one of the walls. I knew that knots compromise the strength of timber, but had no idea that they also have different thermal properties. The temperature-reading at the knot was two degrees warmer than the surrounding wood. It might only have made a small difference, but in the depths of winter that might be the difference between survival or death.
Next, I added some planks to the edges of the hive, effectively creating a ‘double wall’. The planks block my access to the inspection board, but as opening during the winter is likely to let cold and moisture into the hive, it does not seem to be a major problem. Even more so than through the summer, I will rely on the bees’ instinct and ingenuity to solve any problems, without my interference.
The double-wall arrangement still did not seem sufficient. I suspected the outer wall could simply be ‘hiding’ the problem from the camera, rather than providing true insulation. So I filled the cavity by cutting old shirts into ribbons and pressing them into the space between the walls. Four centimetres of wood and fabric separated the bees from the world, and that felt like it was enough.
Thermal surveys are best done at night when the readings won’t affected by energy from the sun. In daylight, I looked at the individual bees. In the infra-red spectrum bees look a little like glow-worms, but with their heads and thoraxes illuminated rather than the tips of their abdomens. The front end of a bee, where all the thinking and flying and muscle-movement happens, is generally a few degrees warmer than the back end. Watching at the entrance of the hive I notice that each bee shows one of two patterns. I surmise that flight warms more of the body, so the outbound foragers are those with only a warm head-and-thorax, whereas the inbound ones have an all-over glow.