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Bumblebees on warm tarmac

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Joined 2013-10-04

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I am a cyclist and on the sunny days of the late summer I seemed to be finding myself removing increasing quantities of bumblebees that were crawling on warm tarmac roads.  Partly to avoid danger to myself I resorted to raising my eye-line so that I could no longer see them because there were so many!  This might seem naive, but why are bumblebees so drawn to warm tarmac?

     
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Joined 2012-05-24

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Hi Mike,

Firstly, welcome to the Forum !
Secondly, my apologies for my slow response.  I’m getting back to keeping an eye on the Forum after some weeks gap.

Bumblebees are warm blooded when they fly and are active.  One of the things they seem to love doing is to “sun” on warm surfaces, such as a brick wall that has been warmed by sunshine. 
Just a few degrees above ambient seems to be adequate to attract them. 
They could then raise their body temperature to “activity temperature” with less use of body-stored food reserves.

So, I suspect that what you have observed could be bumblebees that are having a free warm-up.

The numbers you saw doing this might have been increased with the late-summer peak of male bees (drones) who seemed to hang around at good numbers this year, then drop off rapidly with the significantly colder weather we got from the second week of September.
Male bees have no stings, so you are not at any risk of being stung: but to be sure of this you’ll need to get good at identifying them !

Any comments ?

Yours       Clive