It was outside the Podiatry Clinic in Walker Close, Ipswich. The time was ten o’clock on the morning of 24th June. Not exactly the circumstances in which you would expect to see a hirsute couple engaged in propagating the species. I might have shielded my daughter’s eyes but it was her sharp young senses that detected them first.
We were just leaving the building when Rebecca drew my attention to the metal push plate on the outer door we had just come through. On hearing the buzzing of a bee she had glanced round and spotted it clinging to the silvery surface. It was a large queen, her fore legs grasping at what little purchase the uppermost edge of the plate afforded her. Something appeared to be obscuring the tip of her abdomen preventing identification of the species from where I stood, several metres away. Moving closer I realised that the offending body was in fact a much smaller male of the buff-tailed bumblebee, Bombus terrestris, and that the pair were in copula. I had recently read that mating pairs are rarely observed in the wild (Goulson, 2003) so clearly I could not pass up the opportunity to record their behaviour. However, I was not in the best place to continue my observations. I was already attracting some attention from other visitors to the clinic (much to the embarrassment of Rebecca) and it was likely that, disturbed by the opening and closing of the door, the bees would soon move to a less accessible spot. Also I needed to get Rebecca back into school so I collected the pair into a plastic vending machine cup and sealed it with cling film for the journey home.
Thirty five minutes later, in the safety of my study, I released the bees, still in copula, onto the seat of a chair and reached for my digital camera. Unfortunately I had not kept the batteries charged and only managed a few preliminary test shots before they were completely run down. Even the best of these was not of a quality suitable for publication. I reverted to pencil and notebook and spent approximately fifteen minutes observing the bees before they eventually separated.
Although written thirty years ago, the description of mating in bumblebees given by Alford (1975) still accurately summarises the few studies on the subject. The male initially lands on the thorax of the young queen with enough force to knock her to the ground. He then climbs onto her abdomen grasping her with his legs whilst attempting to copulate. If he is successful the queen protrudes her sting that the male avoids by releasing his hold and falling backwards. However, the couple remain joined at the tip of their abdomens where the male genital capsule is locked inside the female genital tract. Clearly the initial stages of this process had been achieved shortly before I first observed the bees in Ipswich although I could not see the protruding sting.
The fact that the bees were mating approximately 1.5m above ground on a vertical surface would seem to be notable as, usually, mating is completed on the ground (Goulson, 2003). Although Lie-Pettersen (1901) beat large numbers of copulating pairs of Bombus terrestris from deciduous trees in Norway, Alford (1975) implies this may have been an unusual situation due to a high population density. My observations suggest differently as every time I placed the bees on a horizontal surface the queen crawled away. When she came to a vertical surface she proceeded to climb dragging the male along as well. Presumably, in more natural surroundings, a similar climbing response would be observed when a tree trunk was encountered.
Alford (1975) also reported that young queens are sometimes seen in flight with a male holding on. Goulson (2003) confirmed this, adding that the flight is very clumsy. I too observed the queen’s ability to fly short distances. Her attempts to reach a window 2m distant were indeed clumsy and she eventually achieved her goal in a series of short hops rather than a single flight. When she eventually landed on the window sill she crawled across it and then climbed a net curtain and onto the window, coming to rest on the frame approximately 1.5m above floor level. The bees remained joined in this position, very similar to their initial stance on the clinic door, for several minutes until they eventually separated at 11.00, exactly one hour after my initial observations. Alford (1975) stated that bumblebees remained in copula for periods ranging from a few minutes to an hour or more. My observations on Bombus terrestris agree with these findings, falling towards the upper end of the reported range and above the mean values of 36-44 minutes quoted by Goulson (2003). The prolonged copulation in bumblebees is probably enforced by the male as following sperm transfer he places a gelatinous plug within the female genital tract and prevents her from mating again until his sperm have reached the spermatheca, a journey that may take up to 80 minutes (Duvoisin et al. 1999).
Alford, D.V. 1975. Bumblebees. London: Davis-Poynter.
Duvoisin, N., Baer, B. & Schmid-Hempel, P. 1999. Sperm transfer and male competition in a bumblebee. Anim. Behav. 58: 743-749.
Goulson, D. 2003. Bumblebees: Their Behaviour and Ecology. Oxford: OUP.
Lie-Pettersen, O.J. 1901. Biologische Beobachtungen an norwegischen Hummeln. Bergens Mus. Aarb. 6: 3-10.
Paul Lee, Oakdene, The Heath, Tattingstone, Ipswich IP9 2LX
© 2004 Suffolk Naturalists' Society
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