Amadan's picture

Boring Eristalis

No, I'm not doing these delightful hoverflies down. Instead, I am puzzled by an odd observation of behaviour.
One of the many discoveries in our new home (an old cottage) was my wife noticing sawdust around the windowsill of the conservatory. I found that the pine window frame had two holes in it, one in the "shell", and a matching one in the frame itself.
OK, so I dug out the wood filler and commenced to repair the damage. I left the window propped open for the filler to cure, whilst doing some pruning around the area.
I was surprised to see an Eristalis (I think, species uncertain) visit the repaired spot several times, where it inspected the spot very carefully, and seemed to be "working" in the corner of the frame next to the repair, for several minutes.
Do Eristalis, or any species a twit like me could mistake for one, collect wood for nesting material?