Hi there ... I'm new to all this allotment stuff and have had a plot for nearly 12 months! We have planted 5 fruit trees in a clay based soils and plan to build a cage around them, but would they not benefit from birds and butterflies?
Ask your neighbours... some sites are more prone to bird damage... our site has quite a lot of trees so they tend to leave them alone (fruit trees)...
The 20mm mesh is plenty wide enough for bees and butterflies to do the buisness..
And welcome to the madhouse...
;D