Puzzling bumble bee behaviour in summer

[Janec]

This summer I noticed a bumble bee nest in the ground down the side of a tree root.
I don't know what kind they were but they had orange bums.
The nest seemed to be occupied by two completely different sizes of bee although to my middle aged eyes apart from that they looked the same. On several occasions I noticed what looked like one of the smaller bees attacking one of the much bigger bees which tried desperately to escape and shake off it's attacker. Would they have been two different types trying to claim the nest or am I being naive and they weren't fighting?
Will they return to the nest next year, if so I'll make sure the hole is kept open (the tree root is in a used gravel path).
Thanks
Jane

[Geoff F]

Was the bee all black with a red/orange rear end, Jane, which would suggest Bombus Lapidarius. Or did it have bands of yellow as well, in which case it might be Bombus pratorum. That is a rather basic description but it might start you off when looking for a firm identification.

There are a couple of alternatives to the scene you witnessed. Firstly were they mating? Males are smaller than queens and in some species they look rather different; particularly so with B. lapidarius.

The second possibility is that one was a Cuckoo Bee. There are a variety of species which lay eggs in the nests of other bees or take over an existing nest after killing or expelling the resident queen.

B. rupestris is a cuckoo of B. lapidarius.

A summer queen will not live until next year but some of her offspring will produce next year's brood; and they will be looking for suitable nesting sites. They may reuse an existing nest but the chances are they will create a new nest nearby, if the conditions are suitable.

That is a very simplified description of bumble bees in general and different species tend to live slightly different lives; but it should give you a basic idea.

[Janec]

Thanks Geoff,
I think they were all black with an orange rear end. I don't remember any stripes and I wasted quite a lot of time watching them going in and out (when I should have been working)
Would there have been more than one queen as I saw this on several occasions?
If it was mating the female certainly didn't look very happy about it and tried to scrape the male off with her legs and against obstacles (do bees get headaches?)

[Geoff F]

I was rather hoping that one of our bumble experts would pick up this question. My knowledge of this family is a little basic.

B. lapidarius males are quite different from queens and have some yellowish bands on the thorax. Although B. rupestris does take over the nests of B. lapidarius that action is more likely to happen inside the nest. And they are mostly limited to southern counties (approx Bristol to a little north of London) although they appear to be gradually moving north.

I suppose it is quite possible that if good nest sites are scarce there could well be strong competition between new queens.