Mating red-tailed bumblebees

Amongst bees, bumblebees have very long copulations when compared to honeybees and solitary bees. Up to three hours have been recorded for Bombus lapidarius, the Red-Tailed bumblebee, closer to half an hour for B. terrestris. I came across these paired Red-Tailed bumblebees (above) yesterday in the wildlife garden. The brightly coloured, smaller male was simply riding the female, and she bumbled along, feeding on knapweed and heavily flying between flower heads. Females would be expected to be very vulnerable to predators during this time, where they are also very obvious. Although they can actually fly, slowly and clumsily, their sting is immobilised by the male's genitalia. Illustrating this increased vulnerability, the couple of the same species below was squished on a busy pavement last summer.

Why do bumblebees mate for such a long time? Could it be that they need a long time to successfully inseminate the queen? Apparently not, as successful sperm transfer happens in a few minutes when it has been measured. Another reason, is that males transfer not only sperm during copulation, but a 'copulatory plug', which physically hampers further copulation by the female and includes chemicals that make her unattractive to other males for several days, although apparently this plug is also transferred in a matter of 10 minutes. A lengthy copulation might also include the time necessary for the sperm to travel to the female's spermatheca, so the male would be increasing his chances of paternity by guarding his partner. Due to the dangerously long copulation, the copulatory plug dissuading further partners, and the still puzzling effects on her hibernation success and colony fitness due to multiple mating, Bumblebee queens only mate once, with one of the few exceptions being the tree bumblebee (Bombus hypnorum).

More information:
Brown, M., & Baer, B. (2005). The evolutionary significance of long copulation duration
in bumble bees. Apidologie, 36 (2), 157-167 DOI: 10.1051/apido:2005008