Gangs of male bumblebees

During the hot weather in the first few weeks of August, we took to sitting in the shade by our pond with our mid-morning coffee.  Butterflies, bees and hoverflies passed by, sometimes stopping on nearby flowers, but the main attraction was a large clump of lavender.  With its many purple flowers and grey green foliage, it lent a sweet scent to the air as it cascaded down a rough stone wall by the path and was thronged with medium sized bumblebees.  The heat seemed to stimulate them and they moved continuously from flower to flower, stopping only briefly to feed.  Each time they moved to a new flower head the stem dipped as it took their weight only to spring back as it adjusted.  Sometimes the light reflected off their wings like glittering fragments of glass.  With all this activity, the lavender clump appeared to be alive.

In the middle of the day, up to ten bumblebees could be seen moving about the lavender clump at any one time and with their black, yellow and white striped furry bodies they looked superficially to be of the same species, probably buff-tailed bumblebees (Bombus terrestris).  Photographs supported this identification and examination of their back legs showed they were males.  These male buff-tailed bumblebees will have emerged from a nest that reached maturity during the summer and males, once out of the nest, cannot return and spend their time searching for virgin queens and feeding.  Dave Goulson has likened the gangs of male bumblebees drinking nectar on flowers such as lavender to groups of men propping up the bar in a pub. 

I wondered what they did at night and one evening I walked past the lavender and found three immobile male bumblebees attached upside down to flower heads (see pictures at the head of this post and below).  This was their roost and one of more was there roosting on many subsequent evenings.  Male bumblebees have a short life, a few weeks, and by the third week of August numbers had dropped and those that were still about looked rather sluggish.  Small brown Common Carder bees (Bombus pascuorum) began to take over the clump but that was also beginning to show signs of age.

This short video gives an impression of the actiivy on the lavender

Buff-tailed bumblebee feeding from lavender. The shape of the back leg is characteristic of a male.

Another of the bumblebees

Roosting bumblebee (seen early on the morning of August 15). The lavender is showing signs of age.