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Honey Bee Biology

Unusual Winter Cluster Behavior: Finally Observed with Thermal Imaging

- December 1, 2017 - Wyatt A. Mangum - (excerpt)

Thermal Imaging of bee winter clusters

During a dark and bitter cold morning of last January 2017, I had just sprinted to the back door of the house. I was running from the bee house by my home apiary. Not because of the bees, but rather I ran from seven measly degrees above zero, the only ones remaining at 4:00 a.m. I had been inside the bee house where I keep observation top-bar hives of various sizes.

Classes were on break over the holiday. Suzanne was away visiting her relatives, and I was book writing and bee watching 24/7. For this late-night session of bee watching, I was taking thermal images of winter clusters in observation hives with 12 combs, which are more like a regular-sized colony. I had a Flir thermal camera attached to my iPhone. After a stealthy and tedious photo session being careful not to disturb the clusters, my fingers stung with cold. The delicate little touch controls on the iPhone quit responding to my light tapping. Maybe the little phone thinks I’m frozen–dead, I thought, in the darkness of the bee house. Feeling the burning in my fingers growing, I wondered if my phone might be right.

I slipped quietly out of the bee house and tried the controls again. Nothing. I could not even take a picture. Driven by the intense pain in my hands, I just bolted for the house, aiming for the backdoor light, just a dim spot from the bee house, which promised warmth and recovery. I had to return as soon as possible. The clusters were behaving in strange ways that I had never seen.

These 12-comb observation hives were still relatively new to me for winter observations. They were nothing like my usual single-comb observation hives. I have managed dozens of them in the bee house. (The bee house can hold 30 of them.) I was still testing out a pair of 12-comb observation hives (see Figure 1). In the early fall I put a top-bar colony in the observation hive. Under normal conditions, the bees do not build comb in the winter. So the bees do not connect the sloped-edge combs from the top-bar hive to the vertical glass walls.

I can easily remove the glass sides of these observation hives. Nothing but duct tape holds the glass to these larger observation hives. These are special research observation hives, not like typical ones viewed by the public, where the glass provides ultra-safe viewing without bee contact. Rather, I need to enter these hives quickly with glass removal in less than 30 seconds, and always with a minimum of bee disturbance.

On a typical frigid January night, a normal winter cluster in a multi-comb observation hive appears as in Figure 2. The outer layer of bees is oriented with their heads into the cluster. Any single bees separated from the cluster have frozen. Notice the bare edge of the combs. Those edges are frozen barriers between the bees. Admittedly the contrast is difficult to appreciate. So here is the same scene shown as a thermal image (see Figure 3) and a close up (see Figure 4). Notice white emanates from deep in the center of the cluster while the surrounding lower parts of the hive are in the cold background temperature in the lower teens.

Before the cold caused my temporary retreat, I had been observing bee behavior that I had only heard by listening from outside of the hives in the apiaries in the cold, and even then the sound was uncommon. Tonight, I first heard it upon slowly opening the bee-house door, just partway in the dark. A restless low hum …