This summer I have found dozens of orange-tailed bumblebees staggering around my garden until they die or get killed by red ants. Their wings don’t seem to work (sometimes they are even just stubs), and they are very confused. It is very distressing to watch, and my cocker spaniel thinks it’s great to eat them. I had to dispatch three yesterday, which was horrible. I wonder if one of my neighbours has been spraying their roses? Any thoughts or suggestions would be appreciated!
I’m guessing your poor Bumbles have been got at by a parasitic fly or wasp, such as Sicus ferrugineus, where the larva of the parasitic fly will live on the contents of the host bee, which apparently & understandably(although I haven’t witnessed it), affects the behaviour of the host Bee leaving it crawling around & unable to fly.
I have moved Red tailed bumblebee (B. lapidarius) colonies a few times to my garden to save them from destruction.
I have also seen bees of this species crawling around on the ground seemingly unable to fly: and it is probably more frequent with this species than with B. terrestris colonies in my experience.
If fully formed it might be that the bees are having difficulty warming up due to lack of food. (They need a thorax temperature of 30 -40C to fly.)
So, you could try feeding them and see what happens. (Sugar solution at about 30% wt wt sugar in water. One drop should suffice.)
It is known that lack of humidity in a nest can result in bees getting deformed wings.
Also, some of the virus diseases that honey bees get can cause wing deformation. Prof Stephen Martin at Sheffield University has said in a Beekeeping Lecture which both he and I attended two or three years ago that his group would be interested in receiving samples of bumblebees affected by deformed wings.
You’d need to ask them how to send the sample in, because dead bees packed in the obvious choice of being protected by plastic are liable to rot in the post !
I hope this helps !