While I generally feel sure-footed on matters of literary greengrocery, I'm at a loss on this one. How would a pedant write a sign alerting others to the presence of nests of wasps to make other pedants maximally happy?
You can use the words "Danger!" "Wasp" and "Nest" and can suffix one or more "s" and an apostrophe to any of them or refrain from doing so, as you see fit.
I'm aware of the irrelevance of such considerations in the grand scheme of things.