In our "butterfly field", we mainly have the usual Common Milkweed, with a couple stems of Tall Green Milkweed mixed in. In our other field, there's quite a bit of the Tall Green, but most of it gets mowed a couple times a year (except for what's on the steep pond dam). I've never paid a whole lot of attention to the TG, because I've only found one cat on it before, and a source in one of the butterfly groups told me the females won't lay on it because the cats won't eat it, and that the lone cat was probably a fluke; having crawled there looking to pupate or something. So while I give some of it a cursory glance once in awhile, I'm mostly just peering at it for it's unusual flowers than looking for cats.
But as I've said already, we've not been seeing any females and we haven't found any cats on the Common after that first small bunch. So imagine my surprise when I was out checking the Common and noticed a giant cat on a TG from halfway across the field; and then another, and another, and another! Nearly a dozen found in just a few minutes; and of various instars, so the girls have been sneaking in multiple times!!
So we have the four BST's (two have now pupated) and a dozen Monarchs in the tubs. I have to leave for a few days, but I plan a thorough TG-checking expedition when I return!!