Morg,
When you say weldmesh, aproximately what mesh size? Chickenwire any good? I would like to let in as many insects as possible while keeping out the undesireables (I sound like a Home Secretary).
Jenn,
I think it's both, but possibly mostly climate. Most of the UK is pretty mild in comparison to the US - it just wouldn't be worth doing this in Wisconsin, and in Florida, you can just walk out of the door and have all the species you want anyway!