Hopefully it will kill off the iguanas... Ain't that a thing?
Seems I heard tell of em dropping out of the trees on one cold snap or another... 
Actually, it doesn't kill the iguanas (normally) but puts them into a comatose state or very sluggish when temps start dropping into the 40's. I haven't see the really big one or any of the babies for a couple of weeks. I put rosemary along the seawall and that's supposed to keep them away.
It's not going to bother me a bit of this cold snap does kill them; tonight we are supposed to dip down to about 37. That's plenty cold to keep them from moving around at least.
Yes if they are in a tree, they can fall out when cold weather hits. I've never witnessed it, but I've seen pictures.