Not all monarchs migrate. Migrating populations and non-migrating populations coexist in many areas. Monarchs are year-round residents in Florida and monarchs migrate to Florida and Gulf coast areas, and can often continue to breed and survive the winter. The monarch population in Florida may be a result from migratory butterflies that do not migrate north in the spring. These locations provide access to nectar plants. If there is a hard frost in these areas they do not survive. Asclepias curassavica, an introduced annual ornamental, provides larval food if native species are unavailable, although because of the risks to monarchs from the spread of the parasite, OE, this plant is not recommended for planting.Monarch Joint Venture. 2016. Potential risks of growing exotic (non-native) milkweeds for monarchs. This 'potential' risk does not have solid scientific support. If cared for properly, and if the Monarch eggs laid on it, are brought in to be raised through their life cycle, these Monarch butterflies can have an infestation rate as low as 5%. There has been no scientific study that includes this data of the low rate of O.e. in Monarchs raised from eggs. http://monarchjointventure.org/images/uploads/documents/Oe_fact_sheet.pdf Year-round breeding of resident monarch populations exist in the Caribbean, and in Mexico as far south as the Yucatán peninsula. Surprisingly, monarchs do not migrate over most of their global range. Tagging records demonstrate that the eastern and western populations are not entirely separate. Arizona butterflies have been captured at overwintering sites in both California and Michoacan, Mexico. In some instances monarchs from Arizona and New Mexico were found overwintering in California and in Mexico.
