Danaus plexippus

Smith et al. (2005) recognizes two subspecies, Danaus plexippus plexippus in temperate North America and D. p. megalippe in Caribbean, Central, and South America based on their migratory behavior, size, and wing patterns; however periodic gene flow between these subspecies likely occurs, as evidence supports the hybridization between D. p. megalippe, and D. p. plexippus, at least in Cuba (Smith et al. 1994; Smith et al. 2005; Altizer and Davis 2010). Further, while molecular analyses by Brower and Jeansonne (2004) found no phylogenetic structure among monarch populations, there is some evidence that the migratory population is genetically distinct from the non-migratory population (Zhan et al. 2014). As such, whether monarch populations should be recognized as distinct subspecies is a question that warrants further study (Altizer and Davis 2010). We follow Smith et al. (2005) and include all temperate North American populations as part of subspecies plexippus. Taxonomic separation of eastern and western populations of subspecies plexippus is not warranted based on current genetic information (Lyons et al. 2012). The U.S. Fish and Wildlife Service evaluates the monarch butterfly at the species level.

This subspecies has a large range and number of known occurrences in both its native overwintering range and areas where it is not native, but it has experienced severe long and short-term population declines and is subjected to many, ongoing threats.

North America forms the core of the monarch’s range but the overall range extends through Central America to northern South America (USFWS 2024). This species also occurs in Hawaii, Australia, several Pacific islands, parts of Asia, Africa, and southern Europe (Zhan et al. 2014). Several populations outside of the Americas appear to be nonnative, originating from introductions that are thought to have occurred in the 1800s (Vane-Wright 1993), but Zhan et al. (2014) suggests that introductions may have occurred much earlier. The North American populations (subspecies plexippus) are strongly migratory, resulting in vastly difference seasonal ranges with essential overwintering areas limited to coastal California and the mountains of central Mexico (USFWS 2024). The summer range includes portions of the conterminous U.S and the southern portions of all Canadian provinces bordering the US where milkweeds occur. There are some non-migratory populations along the Gulf of Mexico from the Florida panhandle to eastern Texas and the Carolina and Georgia coast as well as along the coast of California in the west; these populations are thought to be small and potentially population sinks that depend on augmentation from migratory individuals to persist, but they are understudied (Howard et al. 2010; Crone and Schultz 2021; USFWS 2024). Subspecies megalippe is found in the Caribbean and Central and South America, from Colombia to central Peru (Smith et al. 2005).

The number of occurrences of this species is estimated based on native overwintering sites and non-migratory island populations of subspecies plexippus and populations of subspecies megalippe in the Caribbean, Central, and South America. The eastern North American population has been documented as overwintering at 19 sites in the states of Michoacan and Mexico, Mexico (Vidal and Rendon-Salinas 2014; USFWS 2024). The western North American population has been documented as overwintering at more than 400 sites, mostly along the California coast, but in 2024 only 109 hosted at least one monarch and the number fluctuates annually (Monroe et al. 2014; Xerces Society 2025). Breeding habitat for the migratory populations is found across much of continuous North America and there are many thousands of patches where monarch larvae occur in summer, but these are not persistent populations, and most have only a few adults (USFWS 2024). There are extent populations in at least 90 countries, islands, and island groups outside of contiguous North America (USFWS 2024). There are also some non-migratory populations along the Gulf from the Florida panhandle to eastern Texas and the Carolina and Georgia coast as well as in areas of coastal California (Howard et al. 2010; Crone and Schultz 2021; USFWS 2024). There are an estimate 190 occurrences in the Caribbean, Central, and South America using a 10 km separation distance and from 2024-2025 alone (RARECAT; GBIF 2025).

This species is threatened by habitat loss due to development, agriculture, and logging, increased fire intensity and fire suppression in prairies, as well as directly by pesticides and indirectly by herbicides through loss of its host plants, and climate change, including increased droughts and temperature extremes (Walker et al 2022; USFWS 2024).