There's a whole science to monarch/milkweed preference ��" that is, a lot of research being done, by Monarch Watch, the University of Minnesota, and others. Also, many anecdotal observations by many amateurs suggest egg-laying monarchs prefer certain species when they have a choice.

My own observations agree with yours, to some extent. Compared to syriaca and tuberosa, monarchs will almost always prefer incarnata. I'm surprised, though, that your speciosa doesn't attract at least an equal number, as mine do. I have no experience with C. laeve, although I would suspect that it would be less attractive than Asclepias species in the same setting.

In my yard, the most-preferred native species, by far and away, is A. sullivantii. I have a dozen species of milkweed on the property, and in 2012 (drought year) and 2013 (recovery year), I'd say 90 percent of all eggs were laid on Sullivant's milkweed in preference to all others. NONE were laid on common milkweed during the latter half of both those seasons.

This year, swamp milkweed has been about equally popular with Sullivant's, but I also planted a lot of A. curassavica (tropical) as an annual amongst the swamp milkweed. Curassavica is very attractive to egg-laying females, and I think it drew some to the incarnata. But the Sullivant's was still king.

Tuberosa is very low on the list. Monarchs seldom lay on it if any other variety is available.