It’s winter and I’m thinking about my bees in these recent cool temperatures; my curiosity turned to Google Scholar and searching for the beekeeper and engineer - Derek Mitchell. Here I found Derek’s 2024 paper in the Journal of Thermal Biology - Are man-made hives valid thermal surrogates for natural honey bee nests. This is a highly technical read with an exotic mix of scientific units, but I found take-home nuggets useful to my hobby beekeeping. My goal is not to keep bees in a tree, but to modify my wintering of bees in a thin-walled wood box by learning what bees have, on their own, achieved living in tree cavities.
| Man-made hive | Tree nest | |
|---|---|---|
| Top ventilation | Beekeeper’s choice | None |
| Wall properties | Thin low R-value | Thick high R-value |
| Comb to wall surface | Continuous bee space separation | Comb attached to the wall with a few small gaps |
| Comb to roof surface | Continuous bee space separation | Comb maximally attached to tree cavity roof |
| Comb to bottom surface | Continuous bee space separation made more complex with multiple boxes | One continuous separation |
| Vertical comb length | Single frame height whether using one or multiple boxes | Continuous |
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Using 16 variables adjusted to experimental observation, Derek used computational fluid dynamics (CFD) modeling and compared the convective air flow and metabolic impact to bees in a standard British National Hive (one box of 35 Liters) versus a synthetic tree nest (45 liters).
Derek writes, “bee space above combs increases heat loss by up to ∼70%; hives, compared to tree nests, require at least 150% the density of honey bees to arrest convection across the brood area.”
Derek recommends blocking the bee space above the combs in a man-made hive, which I interpreted as adding a clear plastic sheet resting directly on the top bar frame. I have a box of letter-sized plastic sheets designed for overhead projector presentations - it seems perfect for the task. Stay tuned for how this works out for me as I am over-wintering two hives with a different number of boxes. One hive has two medium boxes, and the other hive has one deep box. I spliced sheets together with tape and trimmed the extended sheet to fit inside my eight-frame box. Each hive received one trimmed plastic sheet beneath its inner cover resting directly on the top bar frame. No doubt the bees will glue the plastic to the top bar frame and this will require some vigorous spring cleanup effort. 🤣
Perhaps you want to give this small modification a try and use different materials (e.g., wood, thick acrylic, or coroplast).
