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Males - voluntary nest departure or eviction?

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Just wondering what research has been done into the question of to what extent males leave their nests voluntarily and to what extent they are evicted by the workers.

My house has an air brick outside the kitchen.  The inner vent to this was blocked off in January 2013 when we had a new boiler installed, and I think the wall cavities had been filled with insulation here many years ago.  Last year and this year we’ve had bumblebess nesting in the space behind the air brick.  Not sure which species it was last year, but this years are definitely B hypnorum.

Last year on a couple of occasions I saw what I was pretty sure was males being evicted.  Towards the end a mass of silken threads appeared around most of the holes in the air brick, so I’m guessing the wax moth larvae were in there.  This year, however, I haven’t actually seen any males evicted, though I have some indirect evidence that suggests that some may have been.

Just wondering what the state of current scientific knowledge on this point was, really.

Thanks
Adrian

     
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Hi Adrian,

I’ve just spotted your post, having just scanned the Forum for the first time in ages.
(It is coming towards the time 2015’s bumblebees started to wake up ! )

I don’t know about the research knowledge, but my own observations might be relevant here.
I occasionally get asked to relocate bumblebee colonies.
Off the top of my head the species involved have been B. terrestris, lapidarius, hypnorum, pratorum and hortorum.

My moving colony protocol involves transferring the comb and bees into a Perspex topped double chamber bumblebee box, then keeping the colony shut in for a day or two, so that when the bees are released to fly they will re-orientate from their new location.

Particularly with lapidarius, where the drones are visually distinct, it is easy to see them flying from such a relocated colony.
When you release such a colony containing males (drones), these always fly out of the entrance tube very quickly after it has been opened; and I can’t remember them re-orientating (circling) much when they leave the new location.

So, I suspect that the males leaving the colony is innate, not driven by the workers hassling them.

Next time I release a colony I will try to remember to video what happens, so the event can be studied at leisure.

I hope this helps.

Clive

     
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Thanks Clive.  To clarify one small point of detail, a few feet below the air brick is a dustbin with a black polythene lid. What I had seen happen a couple of times in 2013 was bees plummet from the airbrick entrance directly onto the dustbin lid.  This clearly wouldn’t have been bees voluntarily flying off!  At the same time, the faces of guard bees could be seen immediately beyond the holes in the airbrick.

     
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Hi again Adrian,

The following information might be relevant to your observations.

Over the last few years I’ve had a succession of re-located Bird Nest Box colonies of B. hypnorum (Tree Bumblebee) positioned at the back of my garage.  (One at a time.)
The boxes are out of the way, but easily and safely watched from about 3 metres away.
This position is also about 2 metres above a row of plastic water tanks (barrels), each with a black plastic lid tightly fixed.
Some years I have also had a sheet of wind-break plastic cloth fixed horizontally above the water tanks, effectively giving a landing area.

One of the regular occurrences is for bee-collisions to occur among the attendant cloud of male bees (drone cloud).
You can hear a low intensity “bang” when collisions happen.
Some of the bees that have landed on the water tanks, or on the plastic sheet, are obviously injured.
The injury is usually a wing that looks dislocated.
These bees often seem moribund and usually die later that day.
Other bees recover quickly, rest for a while, then fly off to re-join the cloud.

Sometimes a male grabs hold of a virgin queen, in an attempt to mate; and these pairs fall to the ground nearby.  Then the queen slowly walks up the nearby surfaces, plants etc and pairing can take place.

It sounds like your bees might have been having collisions etc like mine.

When one of these colonies is active, in the nest box you can see workers(?) keeping guard around the entrance.

How does this fit with your observations ?

Clive

     
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Hi Clive

I can’t discount that possibility, as I did indeed observe exactly what you described on several occasions in 2014, when we definitely did have B hypnorum nesting behind the air brick and ultimately had drone clouds around it for about two months.  But I’m not 100% certain this accounts for my 2013 observations as (a) I have a notion it wasn’t B hypnorum nesting that year and (b) I have a recollection that at least once I did see one bee plummet as if it had been pushed backwards out of the entrance.  Unfortunately these were the formative events in getting me interested in bumble bees, and I was less knowledgeable then and in particular hadn’t studied up on the various different UK species.

Adrian

     
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Hi Adrian,

Although bumblebee nests are much less hygienic than honey bee nests, they do remove the corpses of dead bees and also unwanted larvae.
Assuming that the colony’s entrance (flight point) is above ground level, you can fairly often find dead bees or discarded larvae lying on surfaces beneath where a colony is flying from.
So perhaps it might be that the dead bee you found died in the nest, then got thrown out.

Also, I’ve just had a quick look at my stock of bumblebee books looking to see if there is any mention of male bees being hassled to get to leave the nest.  That is not reported, but there seems to be good agreement that the males leave the nest a few days after they have dried off after hatching; and that having left they never come back.  Recently hatched (but dried out) males can sometimes help with brooding tasks, but not with other colony maintenance.

Honey bee males (drones) are only hassled out of the colony in mid to late August, when they are rejected by the workers: although colonies can sometimes have a few drones about in September.  At other times before this, drones are just regular members of the colony which move freely around the brood area. 
The timing of the “hassle them out” period will probably link with the end of the queen production / colony division season associated with swarming.

Any comments ?

Clive

     
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Interesting point about dead bees.  To be honest, I can’t remember whether the one I saw ejected was dead, though I would suspect it probably wasn’t or I might have thought it less remarkable (and probably would have assumed it was just a worker whose time had come).

PS I’m fairly well clued up on honeybees:  dad and I did a beekeeping course when I was about 14 and then we kept a couple of hives for a few years after that.

     
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A further thought on this question, following some observations of this years tree bee nest and drone cloud today.  At one point I saw a queen fly into one of the holes in the airbrick, at which point two or three of the males went in after her.  A few seconds later they came back out agaim, and I had the distinct impression they were being shepherded back by the guard bees…

(As an aside, something else I’ve noticed with the males this year is that quite often I see a queen come out and fly away, and it’s as if they hardly notice, and I’ve not generally seen any of them fly off after departing queens.  They seem to pay much more attention to queens returning to the nest!)