Those look like Monarch eggs to me.

Here is a link that might be useful: Finding and Raising Monarchs by Todd Stout

Monarchs are eaten by birds. Other insects have no problem with eating them. Prey mantis, dragonflies, spiders, assassin bugs, wasp, etc.

The deal is that the common milkweed is not that toxic. Swamp milkweed is more toxic. Tropical milkweed is even more toxic. As Monarchs age, they lose toxicity when they lose scales, too. Hawks and dragonflies that migrate eat them too during migration.

Here is a link that might be useful: Monarch Butterflies are Eaten by Birds

TMC, there are certain species of perennial milkweeds such as common milkweed (Asclepias syriaca) that spread aggressively by runners once established. Others are much better behaved.

Try some tropical milkweed, Asclepias curassavica. It is an annual in any zone above 9 or 10, I think. Mine is not aggressive at all, very pretty too, and I wean all my hatchlings, feed 1st and 2nd instars on tropical, because of it's high toxicity. Then, they go to common because there just isn't enough tropical to feed the large instars.

Runmede I though that the the glycosides in Monarchs were toxic to all vertebrates? However, non-toxic to invertebrates.

Yes, non-toxic to invertebrates and also many birds still eat Monarchs. Even snakes eat butterflies without a problem, especially in the caterpillar stage.

Here is a link that might be useful: Predation at Overwintering Colonies