Wednesday 7 October 2020

Checking on the Bee Hive

Temperature, humidity and other parameters of bee hives can be measured and provide useful indications of hive status and health.   Here is one example of commercially-available equipment.   

So during the last year I've been monitoring our bee hive.  A Lora system sends telemetry from Arduino-based electronics next to the hive.  Over the last Spring and Summer the temperature regulation was extremely good - usually within one degree, whatever the weather.  During Winter the temperature was highly variable and we wondered if the hive was healthy.  The Adelaide plains are fairly easy for bees during colder months and in previous Winters we left the Super on the Brood Box, however this year we removed the Super and I added extra insulation.  Happily the bee hive looked OK during some physical inspections. 

Hive Temp at end of August 

We didn't need to worry.  The plot shows temperature near the middle of the Brood Box in green, plus external temperature in black, over a one week period. Towards the end of this period the variations seem to decrease and the average temperature is rising.  

Hive Temperature, start of September  

This graph follows directly from the previous.  (My simple plotting doesn't restart the day number partway through the plot, but it's the first week of September.) Amazingly the bees have begun to closely regulate the brood temperature!   From this research,  

Honeybee larvae and pupae are extremely stenothermic, i.e. they strongly depend on accurate regulation of brood nest temperature for proper development (33–36°C).

It seems remarkable that bees can do this.  As warm-blooded mammals we can regulate temperature pretty well. But the bees are doing this for their nursery area, using both active and passive methods.  Furthermore they can turn it on or off.  They don't waste energy in thermoregulation unless there are young bees to look after.  Spring is a busy time in the bee hive!   

Apart from temperature,  we've also looked at humidity in the hive. Thermistors are easy to insert into the hive compared to humidity sensors.  For a more novel experiment, I've tried to measure the level of hive activity.  Last year our hive swarmed a few times.  We managed to capture the swarms and donate them to worthy recipients, but swarming may not be ideal for the neighbours.  So it seems useful to at least know if the hive is more active than usual.  Others have used audio and even video processing methods.  I've tried sensing the bee motion in and out of the hive via light-level variations.    Light Dependent Resistors (LDRs) at either end of the hive entrance measure the instantaneous light levels, which change as bees walk by. The figure below shows typical results over 7 days.  

Hive Activity over one week

The upper plot shows the mean light level on a log scale.   LDRs have terrific dynamic range and during the dark periods (i.e. nights) they even pick up moon light!   The lower plot shows the normalised standard deviation over intervals of about 20 seconds.  The two sensors at each end of the entrance gives rise to blue and green plots, although the green is largely over-written.  You can see that bee activity varies quite a bit from day to day, as the weather changes.  Perhaps the next step will be a temperature compensated plot that provides alerts on unusual activity.  

The activity monitoring started in Winter but the LDRs had minimal protection and failed after a few months. Close inspection shows moisture ingress on the sensor surface.   The encapsulation of LDR devices probably varies considerably.  I'm hoping my current LDRs will last longer - each is encased in the end of a glass test tube to provide more protection. This image shows one end of the bridge over the hive entrance, before installation.  The upper surface sits next to the side of the hive.  

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