Hi hedge witch,
I have tried taking photos but even with my macro lense they just come out as white blobs.
I am going to try to have another go in better light though. I have marked where they are in the garden and am planning to chart their progress next year when they emerge; hopefully I can get some photos of the larvae then.
They are very distinctive once you know what they are and I am lucky to have them elsewhere in the garden so I know what to look for.