Thermal imaging technology works by recording the infra-red energy emitted from surfaces – this doesn’t rely on a light source like typical infra-red photography, but instead measures the radiation given off by both living an inanimate objects. The camera can measure the temperature of these items and display a ‘thermal’ image which shows the gradation and variation between different objects within the field of view. In simple terms – it can show a hot object as white/red whilst cooler objects would be shown as green or blue.
In mid-summer, social bees produce a high density of very busy insects in the nest, so it was no surprise that they stand out a mile on a thermal camera! It was also exciting to be able to understand what individual bees had been doing – for example their temperature signature differentiated those who had recently returned to the nest from those who were standing guard and checking in new arrivals.
Wild Honey Bee Nest
We often encounter honey bees when out looking for tree roosting bats in woodland and this was a prime example! Whilst honey bees are often kept in hives, they can establish wild colonies in features such as this.
I took the following images around sunset so the tree itself was cooling but you can immediately see just how hot the inside of this tree cavity is compared with the surrounding wood. The temperature reading inside the nest was 33 degrees Celsius, whilst the surrounding tree barn dropped to around 25 degrees.
Even at sunset, honey bee workers were still returning to the nest and you can see the white-hot glow of these warmer bees compared with the much cooler bees at the entrance. What is also interesting is the pattern of heat in these recently-flown bees – the flight muscles are in the thorax where the wings are attached and this part is much hotter than the abdomen as you can see more clearly in the video below.
The thermal image gave a nice opportunity to watch guard behaviour in action – some honey bees will take the roll of guarding the nest entrance, positioning themselves on the edge and checking returning bees to ensure that they are welcome. The thermal footage clearly differentiates those bees who have recently flown from those which have not, and you can see the much cooler guard bees intercepting the warmer returning workers as they pass by.
If you’re interested in guard behaviour, you might also like this post from a couple of years ago regarding this behaviour in hornets!
These images and videos come from a bumblebee nest which was situated underneath a loose cobble in the courtyard of our office.
I think the bumblebees are either white-tailed (Bombus lucorum) or buff-tailed (Bombus terrestris) bumblebees – this photo shows one of the worker bees returning with well laden pollen baskets.
The thing that I found most surprising on the thermal footage to see just how hot this cobble got compared with those around it, even though the nest is buried beneath! I assume this is due to the heat rising with the warm air from the next and heating the stone as it passed by.
As with the honey bees, you can see how much warmer the active bumblebees are compared with their environment. Bumblebees have a good degree of control over their temperature. The hairs on their body provide some insulation and they can use their flight muscles – uncoupled temporarily from their wings – to warm themselves up before taking off. This uses the same technique as they use for buzz-pollination of some flowers. This video gives an idea of just how much heat these muscles can generate, allowing some bumblebees to remain active through the winter, flying at temperatures of just 10 degrees Celcius. You can read more about bumblebee thermoregulation here!