Ohhh... that's too bad.
Well, you did your part.

Nature will do theirs.

If it was a praying mantis, the female (if it was a female) may now have the necessary reserves to lay a good cluster of eggs. An ooth (I learned this year that that's what praying mantis egg case is called and use the word as often as I can

) of praying mantis is better for the humans since they will eat many pest bugs (Sacrilege, I know

).
Good luck to your other male Monarch!

I thought I was all done finding eggs or caterpillars, but found another 3rd instar Monarch caterpillar outside yesterday. On the other hand, today, I found our first BROWN/TAN colored Black Swallowtail chrysalis among the ones I'm raising inside. In my experience, the brown ones overwinter, but the green ones eclose this season. Maybe they know something....