I'm not an expert, but I was reading about Monarchs on the Journey North and Monarch Watch sites. They apparently have multi-faceted, multi directional vision that allows them to identify plants visually, and they also have very sensitive chemoreceptors on their legs and antennae that also help. The articles didn't go into much more detail than that.

Martha

Clearly they see, but I think "sensitive chemoreceptors" means that they have a sense of smell--or what we call "smell." Pretty much everything gives off what we call "odor."

I recently watched a monarch lay an egg on a pipevine...!

Fred