Bumblebee Mating

Not exactly seasonal, but I wanted to show you this photo, sent to me by a friend, of Common Eastern Bumblebees (Bombus impatiens) mating last Fall.

The queen is the larger individual, clinging to the edge of a leaf, and the considerably smaller male is hanging below her.

By mid- to late summer, new virgin queen and male bumblebees are produced from successful colonies. These individuals leave the nest and seek each other out for purposes of reproduction.

Mate seeking in bumblebees was first recorded by Charles Darwin who set his children the task of following male bumblebees in his garden to record their behavior. The males of most species patrol a route which they mark with scent produced by their labial glands. The pheromone is deposited on "leaves, prominent stones, fence posts or tree trunks" according to Dave Goulson in his book, 'Bumblebees: Behaviour, Biology and Conservation'. It's not certain exactly how the newly emerged queen encounters the patrolling male. Presumably a combination of the species specific pheromone used for marking and the height above ground of the male's patrolling route provides the appropriate cue.

Observations are few, but presumably the male and female make contact in the air. Then, shortly after coupling, they alight until copulation is complete.

[Photo by Michelle Arsenault]

"Nectar gone. Don't bother"

How do bees, either bumblebees or honey bees, collect nectar and pollen as efficiently as possible? This activity is called foraging, and it is central to the success of any social bee colony.

Honey bee and bumblebee, both foraging on goldenrod

Foraging has been studied best in honey bees, and they are known to use a variety of techniques including aromas, communicating flower location, and scent marking to ensure that individual workers do not waste a lot of time looking for food in unlikely places.

Bumblebees also use scent marking to improve their foraging efficiency. Apparently it works like this. Each bumblebee body is coated with a number of chemicals that serve to waterproof its exoskeleton. As a bee walks over the surface of a flower collecting nectar and pollen its feet leave traces of these chemicals behind.

The next bee to come along can detect the presence of the chemical marker left by the previous forager using sensory organs in its antennae. Bumblebees can often be seen hovering just in front a flower before deciding to alight or instead to move on to the next blossom. It seems that if the bee finds that another has just been working on the flower, it moves on, knowing that the nectar in that flower has probably been used up.

So bumblebees warn each other off a flower that has little nectar left. And honey bees do the same thing. The chemical markers used by different species are fairly similar, and it seems that bumblebees can recognize the 'no nectar' signal left by honey bees.

This chemical marking behavior is probably why you never seem to see bees fighting over a flower. It's a way to ensure that all of them make the best use of their time in the field.

But it also suggests that if you have a lot of foraging honey bees out there marking flowers with 'no nectar' signs, there may not be much left over for the less abundant bumblebees.

[Honey bee and bumblebee photos by D. Barr]

New Bumblebee Sightings in Scotland

Things may be looking up for bumblebees in Scotland. One rare and endangered species for that country, the Great Yellow Bumblebee, was seen farther south last summer than at any time in the past 30 years. This species has been declining for some time in the UK, and populations have been restricted to the far northern highlands and isolated northern islands of Scotland.

A possibly less auspicious sighting came early this year. The Southern Cuckoo Bumblebee (SCB) was spotted near the southern border of Scotland, a new species for the country. Previously the SCB has been common in the UK only near the southern coast of England.

Yes, it's a new bumblebee for Scotland, and a species that seems to be expanding its range rather than being in decline. But is this a good thing for bumblebees as a whole?

The questions arises because cuckoo bumblebees are parasites in the nest of other bumblebees. The normal bumblebee colony lives and grows by harvesting nectar and pollen from flowering plants. Most bumblebees have a number of special adaptations for pollen gathering, the most obvious of which is the presence of a wide, pollen gathering 'basket' on both hind legs.

Cuckoo bumblebees, on the other hand, have no pollen basket and make their living by invading the nests of pollen gathering species. The 'cuckoo' female takes over from the queen of the host species and begins to lay eggs. The workers of the host bumblebee then proceed to rear the cuckoo's eggs as though they were their own sisters. As a result the host colony rears no queens to carry on the next generation. All queens and males produced from that time on belong to the cuckoo species.

So you can see that a new cuckoo bumblebee is a mixed blessing. It can prosper only at the expense of normal bumblebee populations.

The ability to keep track of the gradual changes in UK bumblebee populations is possible largely because of the efforts of organizations like the Bumblebee Conservation Trust. Without a concerted effort to monitor pollinator populations, we are in danger of losing these critical components of our ecosystems before anyone has the chance to take action to save them.

Let's watch those bumblebees.

[The photo above is of the Great Yellow Bumblebee (Bombus distinguendus), taken by James Lindsay and made available under a Creative Commons licence.]