It was only about a month ago when we discovered there is a Swan plant (Asclepias physocarpa) in the front yard.
Imagine our surprise when we saw this today:
Monarch caterpillars only feed specifically on Swan plants. Yes, they only eat one type of food during their caterpillar life! The horror!!!!! ><“
However, a Swan plant diet is definitely the best diet for the caterpillars. Monarch caterpillars and butterflies are poisonous and unpalatable to predators, because of a toxic substance called Cardenolide aglycones present in the Swan plant, which is ingested by the caterpillars and stay retained in their bodies even after metamorphosis.