We get that happening out here too Ian.
A bit of wet weather in Summer months seems to be a signal to the little buggers to swarm. They'll do it for a couple of nights in a row and the following morning the ground is covered in their discarded wings.
People here learn very quickly not to construct anything with a timber frame.
Treated timber doesn't seem to slow them down much either. I've seen them eat the guts out of a Chep pallet leaving behind little more than a thin blue shell.
