A mating ritual by B. hypnorum males
I have had several bumblebee nests in my garden and found many as well over the years in the wild. I have not had any experience of the new UK arrival Bombus hypnorum, other than as garden visitors and sitings outside, nor any experiences of their behaviour. I was very aware that they defend their nests with vigour! I was unsure exactly how this would translate in reality! How far this aggressive defence extended beyond the nest I was not aware. I have been stung by B. terrestris that was just inside the nest entrance hole, it dived out of the nest and stung my neck, and immediately returned to the nest entrance. I was a few feet away, but directly in line of the entrance hole.
‘Swarming’ bumblebee behaviour
With a ‘swarm’ of B. hypnorums outside of each of my two nest boxes, moving up and down, performing circles and figures of 8, others would land on the nest entrance, then fly off to join in the swarm. I watched (and videoed) bees leave the nest and join the swarm. Workers would return with pollen and simply bypass the swarms. Some bees would leave the swarm and go to the ivy behind the nest box, then rejoin the swarm. Diligent defence strategy I believed, searching for potential dangers to the nest. One hot sunny days, many more bees were present and less on cooler days. From very early in the morning to almost dusk, they performed this behaviour. For me, this was completely new behaviour for bumblebees. I made several videos. Then whilst about 8 feet way from one nest, whilst watching the spectacle, I was stung by a B. hypnorum bee just under the eye. Videoing was put on pause!
Misinterpretation of behaviour
I watched a rather persistent green bottle fly try to enter the nest box. A guard bee ran from inside the nest to the outside and tried ram the fly, shooing it off, (though I assume she would have bitten it). The green bottle simply flew up and moved a couple of inches away but still near the nest entrance. It moved to go inside. It was chased again and again by the same bee with the green bottle simply flying out of harms wyto try to eneter the nest box hole from a different angle. It did this several times, in the end the green bottle got the message and flew away. Whilst videoing, (now from a safer distance!), I observed some bees forming part of one swarm move across as individuals to the other swarm and vice versa. “This must be some form of mutual defence of nests” I thought! I found this rather strange behaviour and decided to research defensive strategies of these bees. There was not much to be found until I came across the B. hypnorum Bumblebee Conservation Trust information sheet.
I read about the swarms of bees outside nests. It states that they are drones performing an ‘aerial dance’ like a cloud close to the nest entrance. This behaviour is technically called ‘nest surveillance’ and is a mating characteristic of B. hypnorum. Everything I read fitted my observations. ” Bees join and leave the ‘cloud’ as they move from nest to nest: they are probably following a ‘patrol route’. I had totally misinterpreted the behaviour, being too obsessed and very wary of them ”defending their nests with vigour’ and me being stung to re enforce this belief!
New video I then got to thinking about how and why I was stung. Whilst watching the swarming spectacle, the sting was not of the same severity as the B. terrestris one I had several years ago. This time I was standing in the direct flight path to the nest entrance. I saw this particular bee launch herself out from the nest box, drop down and start to climb up, it all happened so quick. I tried to move out of its way and it collided with me. The sting was not a full blown sting, more of a slight prick really. The bee simply carried on with its outward flight and did not return to the nest box as did the B. terrestris that stung me. It was not a deliberate attack upon me. More my own fault for being directly in the flight path and moving out of the way. Knowing that the swarms were males, therefore stingless, knowing that I did not intend vibrate, knock or otherwise disturb the actual nest itself, knowing my mutual defence strategy was wrong, full of confidence and now out of the direct line of flight, I made this video of the ‘dancing drones’!
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Update…..8th July 5 males still dancing! 10th July 4 dancing. 12th 3 bees, 14th 2 bees, 16th just 1 bee feeling lonely! 18th July 1 dancing bee joined by a bee from the nest this bee was flying around, about 1 minute dancing together then flew back into nest leaving single dancer outside. Short time later a bee again joins bee outside, dance together and one bee returns back into nest. Seen this many times over the weeks, a bee joins swarm from nest box and a bee returns to nest box from swarm. Second tree bumblebee nest now with wax moth larvae inside. 19th, 20th , 21st, 22nd one male dancing. 23rd, 24th 2 dancers. 25th 3 dancers! 26,27th, 1 sometimes 2. 28th, 1-2. 29th 1 sporadically.
Refs. Besides my own observations, videos and experiences;
Hill, C. (2013), “Introducing the tree bumblebee, Bombus hypnorum“, Bumblebee Conservation Trust information sheet.
For more information and to help save bumblebees join the Bumblebee Conservation Trust.