When people buy bees from me they usually ask ‘What can hurt them? Should I be worried about flies or ants?’. My answer is always The Sun. The Sun is one of the biggest killers of native bees in the boxes we choose to house them in.
The following article will show some in hive temperature traces for a strong hive of carbonaria in Brisbane, February 2017. This article will show that even a few hours direct sunlight can overwhelm a colony, while use of shade or insulation protects them.
It’s officially been our hottest Brisbane Summer ever, with an average temperature 2 degrees warmer than usual. And it’s not just QLD. NSW had an average temperature of 44 centigrade for the entire state on 12th February. When we get to these temperatures bees die.
This is the standard advice experienced beekeepers give to the public when there is a heatwave, with temperatures getting to mid to high 40’s.
– Put them in the shade.
– Put a wet towel on them for evaporative cooling.
– Cover them with a Styrofoam box.
– Seal them up and take them inside your air conditioned house.
I used a hoboware data logger with probes placed at ambient in a Stevenson shroud, in a ‘solar indicator box’ located near the bee box, in the mid line of the carbonaria brood, and in the rear honeypot area of the box, also at the colony midline. The box itself is an OATH box, constructed from 25mm hoop pine.
In the traces generated,
Red = brood
Blue = honeypots
Black = ambient
Yellow = Sunshine.
My box is only in the sun from 12:30 to 3:30 each day. Earlier they are shaded by a large Ponciana tree, and in the afternoon they are in the shade of a fence. I thought I was keeping overhead sun off with a styrofoam sheet (25mm) and a brick.
On the first 2 days of this graph you can see the brood temperature climbing as high as 34 degrees. The third day was cloudy. Although the third day was the hottest the brood did not get as hot. This gives us a hint to the importance of shade.
An interesting observation was bees fanning air from at least 8pm to 10pm on night 2, and little temperature dips about 8am on some days.
I used my all weather styrofoam cover. I increased the shade function for this experiment by adding reflective builders foil to the outside of the styro cover. When I provided shade it is remarkable. The carbonaria brood temperature remains at 28 to 32 centigrade which is the same narrow range as my Winter tests.
At this stage I started to get interested. There was a lot of humming from inside during the day, but not much evidence of air going in or out of the ventilation holes. I’m convinced that during the heat of the day ventilation is internal. Brood and honeypot temperature traces suggest the honeypots are used as thermal mass, as a heat sink. The bees I previously saw fanning in the night would be re-charging and cooling that heat sink.
I added the front and rear panels to my all weather styrofoam cover. The results were surprising. Without the cool night air on the sides of the OATH box the colony did not lose heat during the night. I really expected the bees to dump heat during the night by fanning but it did not happen. I don’t know if the bees are not capable of cooling, or if they simply did not try as the insulation had them at a happy temperature.
Bob Luttrell has been monitoring box temperatures since at least 2007. He was kind enough to provide a temperature and humidity trace from carbonaria, Toowong, February 2017. Ambient temperatures were similar to my own. I was particularly interested in data from the INPA box as it has thermal mass built in, as a lump of concrete under the lid. It also displays thicker timber than the OATH, and a reflective heat shield which shades the box walls. In this box brood temperatures fall within the 28 to 32 degree optimal range. The bumpiness of the temperature trace shows that the bees are fine tuning their conditions throughout the day with little regard to outside temperatures.
There is some controversy regarding styrofoam covers in Summer. Some people love them while others think they are heat trapping ovens. Some people swear they must be white while others paint them forest green to blend into the garden.
My tests show that dark coloured styrofoam boxes (25mm) absorb high amounts of heat from the Sun. White is good, and the best effect is using builders foil on the OUTSIDE of the cover.
I really do recommend to all those people with forest green and other coloured covers to re-paint them white!
It’s not so much the ambient temperature that is deadly to our bees, it is a combination of colony strength, box wall thickness and construction methods. The Sun shining on the box compounds these problems and makes things much much worse. I am happy to throw out the old advice of “Sun up to 10am is OK”. I advise full shade in Summer.
Bee boxes and covers can be any colour providing it is white.
Sun is BAD
Shade is GOOD
Thermal mass is GOOD
INPA boxes are GOOD
Looking at the data, if I had heat wave conditions forecast. I would remove my styrofoam cover at night and replace each morning. I would use builders foil on my cover. I would look to incorporate thermal mass, perhaps as a brick or bottle of water placed between the box lid and the styro cover.
The other interesting thing is that T.carbonaria bees can control the brood temperature within a tight range of 28 to 32 degrees in both Winter and Summer, providing the box in which they are housed has both thermal mass and insulating properties. Box builders and bee sellers must continue to strive to build better boxes, and monitor their boxes with temperature data.