I discovered 2 interesting articles by Derek Mitchell (PhD Candidate in Mechanical Engineering at the University of Leeds), one is intended for a general honey bee audience, the other a hard-core engineering-science article. This blog post contains 2 images from those articles.
- Honeybees cluster together when it’s cold – but we’ve been completely wrong about why
- Honeybee cluster—not insulation but stressful heat sink
Facts about bees wintering in thin-wall wood hives:
- bees move from the hive edges towards the center of the hive to form a cluster
- as temperatures fall, the cluster shrinks - see the image from Derek's article
- the cluster core is hot compared to the cluster periphery.
- bees in the core consume honey and keep bees in the periphery warm.
- in extreme winter temperatures, bees on the periphery risk death by hypothermia
- the cluster periphery is denser than the core
Derek writes, "Since the early twentieth century, the outer layer (mantle) of honeybees (Apis mellifera) in the winter cluster has been said to insulate the cluster core."
A shrinking cluster increases density, reduces porosity, and increases heat loss. Here I'm using porosity to describe the amount of empty (air) space, or porosity = empty space ÷ total space. Typically a thermal insulator reduces heat loss by trapping air and is therefore low in density. The higher density cluster periphery is not a thermal insulator - has never been a insulator. Beekeepers need not stress bees in extremely cold temperatures when insulation is readily available.
- take a quick look in beekeeping catalogs and you'll discover flexible hive wraps - flexible wraps roll-up for easy storage and reusable next winter
- solid foam board insulation for home improvement is available for purchase or free as building waste
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