When you think about ways to attract butterflies, this generally involves planting flowers that supply nectar for the adults or leaves for the caterpillars. However an alternative technique is to offer salts, especially sodium, which butterflies crave because their vegetarian diet is rich in potassium but not sodium. This is different from the ancient myth that you can catch a bird by putting salt on its tail. It is no myth that butterflies have a powerful attraction to salt.
You will notice this fact if you carefully observe the behavior of butterflies. For example this week I was biking along a rail trail which also allows horses. It was immediately obvious that butterflies are attracted to the dung of horses. I attach a photo of a tiger swallowtail that was “puddling” on horse dung to obtain the salt rich fluids, which may be disgusting to us, but life-giving to salt starved butterflies.
After working in the yard I took off my sweat-soaked shirt and hung it on a rail to dry. A red spotted purple butterfly was attracted to it, presumably to drink the salt-rich sweat.
It seems quite likely that butterflies recognize the smell of dung and sweat and seek out the sources to obtain salts. I have even had butterflies light on my arm and drink the sweat.
You can also put out a patch of damp sand with sodium chloride added as a butterfly attractant.
So buy a horse, or get sweaty, and bring those butterflies into your yard!