To save honey bees we need to design them new hives

Derek Mitchell The Conversation Sept 9, 2019

Honey bees are under extreme pressure. Beekeepers in the
US have been losing and then replacing an average of 40%
of their honey bee colonies every year since 2010, a rate that
is probably unsustainable and would be unacceptable in
other kinds of husbandry. The biggest contributor to this
decline is viruses spread by a parasite, Varroa Destructor.
But this isn’t a natural situation. The parasite is spread by
beekeeping practices, including keeping the bees in
conditions that are very different from their natural abode of
tree hollows.

A few years ago, I demonstrated that the heat losses in man-
made honey bee hives are many times greater than those in
natural nests. Now, using engineering techniques more
commonly found probing industrial problems, I’ve shown that
the current design of man-made hives also creates lower
humidity levels that favour the Varroa parasite.
Natural nests inside tree cavities create high humidity levels
in which honey bees thrive and which prevent Varroa from
breeding. So if we can redesign beekeeper hives to recreate
these conditions, we could help stop the parasite and give
honey bees a chance to recover.

The life of the honey bee colony is intimately entwined with
its home. We can see this from the sophisticated way honey
bees choose nests of the correct sizes and properties, and
how hard they work to modify them. In fact, the nest can be
seen as part of the honey bee itself, a concept that in biology
is known as an “extended phenotype”, which refers to all the
ways a creature’s genes affect the world.
Perhaps the most common example of an extended
phenotype is that of the beaver, which shapes its
environment by controlling the flow of water with dams. Nests
enable honey bees to similarly adjust their environment by
controlling the flow of two fluids – air and water vapour – plus
something that acts like a fluid – heat.

The honey bees select a tree hollow with an entrance at the
bottom that makes rising hot air inside the nest less likely to
escape. They then modify it by applying an antibacterial
vapour-retarding sealant of tree resin over the inside walls
and any small holes or cracks. This further prevents any
warm air leaks and helps maintain the right level of water
vapour. Inside the nest, the bees build a honeycomb
containing thousands of cells, each of which provides an
insulated micro climate for growing larvae (baby bees) or
making honey.

Unnatural designs Despite the importance of nests to honey bees, the hives we
build them bear little resemblance and have few of the
properties of the natural tree nests European honey bees
evolved with. In the 21st century, we’re still using hives
designed in the 1930s and 1940s, based on ideas from the
1850s. Natural nests were only scientifically surveyed as
recently as 1974 and research into their physical properties
only began in 2012.

Man-made hives are squat and squarish (for example 45cm
high), constructed from thin wood (under 2cm thick) with
large entrances (around 60cm²) and often large openings of
wire mesh underneath. They were designed to be cheap and
for beekeepers to easily access the bees and remove the
honey. In contrast, European honey bees evolved with
natural tree nests that are on average tall (around 150cm),
narrow (20cm) with thick walls (15cm) and small entrances

Man-made hives versus natural nests. Derek Mitchell

In order to assess how well man-made hives recreate the
conditions of natural nests, I needed to measure the flow of
fluids (air, water vapour and heat) around them. To do that, I
turned to an aspect of physical science and engineering
called thermofluids, the study of liquids, gases and solids of
combustion, and changes of state, mass and energy

In the honey bee nest, this means the “combustion” of sugars
in honey and nectar, the evaporation and condensation of
water, and air flow through the nest. It also includes
everything being transported by the honey bees through the
entrance or leaking through the walls.
The various barriers that honey bee nests create can be used
as convenient boundaries in mathematical models of the
energy needed and humidity produced inside the nest. My
new study combines these models with data from
experimental research on the thermal properties of honey
bee nests and hives and behavioural studies on how honey
bees ventilate their nest.

This enabled me to compare the average humidity in man-
made hives and tree nests with that needed by honey bees
and their parasites. I found that most man-made hives have
seven times higher heat loss and eight times bigger entrance
size than tree nests. This creates the lower humidity levels
that favour the parasite.

My research shows the role of the honey bee nest is clearly
far more sophisticated than just simple shelter. Simple changes
to hive design in order to lower heat loss and
increase humidity, for example using smaller entrances and
thicker walls, could reduce the stress on the honey bee
colonies caused by Varroa Destructor. We already know that
simply building hives from polystyrene instead of wood can
significantly increase the survival rate and honey yield of the
bees. More research into the thermofluidic complexity of
nests would allow us to design the optimal hives that balance
the needs of honey bees with their human keepers.

This article has been amended to make clear that the
average 40% of US honey bee colonies lost each year are