The weather in parts of Florida are tropical enough that Monarchs can live and breed there all year. They cannot breed in Canada and the US where the temps go down below freezing. They cannot withstand freezing temps for more than 3-4 days. Dr. Urquhart the Monarch scientist from Canada said that he calls this population nomadic. They spend their life in those coastal area until spring and he wrote that some would actually return north.
There are many species of butterflies that migrate south in the winter and then return north in the spring when temps warm up. Red Admirals, Painted Ladies, Variegated Fritillaries, Buckeyes, etc. But, the Monarch makes the longest journey south of all the butterflies.
Herndon, VA (USA)
Take care of the small things....