Although deceptively bright, it was very chilly outside today (about 8C max) and raining on and off - so we didn't expect much bumble activity. So, I planned to complete some infrastructure changes instead.
This consisted of abandoning our "cloche" nest site following the death of QB2012-02 for a new strategy (we'll use it for growing tomatoes, peppers and strawberries - the bees will love that ☺). The new strategy is to relocate the nest box along our garage wall and create a tube system to provide entrance holes amongst tufts in the lawn. Indeed, we saw 3 brave bumbles around the house and garden today looking for rest / nest sites. 
One big bufftailed Queen surprised us by doing a grand tour of the exterior of the house - check along all the walls, even windows on the top storey. It's encouraging that they will extend their search to man made locations, but what we need to do is figure out what is actually appealing to them. More is known about the natural environments they choose and how to mimic those environmens with a nest box (see the rest of this post). But less is known about how to do the same for manmade features.

Building a tube system

In order to maximise chances of a queen discovering and entering our nestboxes, I wanted to increase the number of entrance points available in the garden. This would also allow us to try different disguise/visbility strategies on the entrace to see which ones the bees favour. 
I built a tube "connector" which allows 3 incoming tubes to meet in a box, and then exit in one direction towards the nest box. When the bumblebee is in the dark tube, it is is tricked into thinking it is heading underground into our lovely warm, dry nest chamber. Total length of the tubes from one entrance to the exit into the box is about 80cm - a distance that Bombus Terrestris should be comfortable navigating to get "underground" (indeed, they should be delighted with it). 
entrance tube connecting systemThe construction is self-explanatory.
Next I filled the remainder of the box with packing material. This is just a precautionary measure to ensure there is no big cavity in the box: we don't want bumble stopping and setting up nest in this box! (There is no easy access into it anyway - it's an additional precaution). 
filled with packing to ensure there is no cavity
Then I taped and sealed the system to make it waterproof and installed it outside. 
revised nestbox site setup with "triple entrance" systemAbove you can see both our nestboxes with their entrance set ups. The box on the left is completely buried under the expanding foam shelter and the entrance tube extends out to the lawn, just bottom left of the heather by the leftmost high-viz cane. 
The box on the right is as yet unprotected (next job!) and the tube extends to the splitter box just behind the potted grasses on the right. The 3 tubes extend as follows:
  1. left of the 2nd heather in from the right
  2. between the 2 grass pots on the right
  3. to the right of the rightmost heather pot
Here's a close "bee's eye" view:
bee's eye view of entrance holes
Note that we are trialling different marking arrangements - does a high visibility marking improve or decrease atttractiveness? 
entrance on our second nestboxFor completeness, above is the entrance hole to our left-hand nest box. Surely a queen would spot this and want to explore it! 

Queen Capture

We are developing revised tactics for the capture of queens so that they are less stressed and more inclined to explore and stay in the nest boxes. To that end, instead of using jars to capture them, we have built these tubes (kindly suggested by George Pilkington) that can be placed over the queen while she is exploring a hole in the ground/undergrowth. It is totally dark, which will keep her calm, and while she is in it, she is more likely to think she is still underground. Then we can carefully bring her back to the nestbox and introduce her with much less trauma. 
The red window allows us an additional check to see she has climbed into the tube - bumblebees do not see deep red light.
bumblebee queen capture tubes 
We are looking forward to trying this once the weather picks up!