Monarchs In South Florida

Understanding monarchs in South Florida is a complex and confusing issue. Most information that you will read online about the monarch butterfly status and what to do to help them may not be appropriate in South Florida. This is especially true about planting milkweed to help the declining migratory populations of monarchs. Below is information based on the best available science to help you better understand the dos and don'ts when it comes to keeping monarchs healthy in South Florida. 

Basic facts to know about monarchs in Florida:

1. Some of the Eastern monarch population moves back and forth through the panhandle region of North Florida on its annual migration to Mexico and is believed to have been on a trend of population decline. Some of these monarchs go down the penisula of Florida in the winter and might migrate across the Gulf to Mexico, continue on into the Caribbean, stay in South Florida, and/or migrate back north in the spring.

2. Most native milkweeds in Florida go through cycles where they seasonally die back during the winter, which encourages continued migration of monarchs through the region. Some small numbers of native milkweed species in natural areas can remain present during the winter in South Florida that can sustain a small non-migratory population. 

3. The non-native invasive tropical milkweed stays present year round in Central and South Florida and does not die back like our native milkweeds. When migrating monarchs encounter tropical milkweed it interupts and stops their migration, induces them to begin reproducing, and shortens their lifespan. This has actually led to an abnormal increase in the population of monarchs in South Florida.

4. Since the non-native invasive tropical milkweed does not die back, it has began to accumulate large amounts of the spores of a very harmful protozoal parasite to monarchs called OE (Ophryocystis elektroscirrha). OE can cause monarchs to be unhealthy, deformed, and/or die. Tropical milkweed in South Florida is causing an unnatural reservoir for OE and it now infects around 90% of monarchs in South Florida. This leaves our resident and migratory monarchs sick, infected, and a source for causing harm to the other poulations of monarchs in North America and the Caribbean. 

5. Only removing tropical milkweed from Florida will eliminate all of the negative effects it has on monarchs and the environment. Tropical milkweed often escapes plantings and spreads to our delicate natural areas. Native milkweeds, when available, are suitable for planting. Florida has over 40 imperiled species of butterflies that need help. There are guides below that offer alternative plants to tropical milkweed that help our imperiled butterflies.

Native Milkweeds found in South Florida

Plant Guide to help Imperiled Butterflies in South Florida

Common Questions & Answers:

Who else uses milkweed?

                Many other species of insects use milkweed. Queen and soldier butterflies as well as some moths use milkweed.

Isn’t there OE on native milkweed, too?

                Yes, however, native milkweeds die back naturally. When the native plants die back, the parasite will too. Non-native tropical milkweed does not die back naturally and can accumulate heavy infestations of the parasite.

Does Florida have resident populations of monarchs?

                Yes, Florida has resident monarch populations. However, monarchs are largely year round residents BECAUSE of the tropical milkweed. Monarchs sense the chemicals from the tropical milkweed and break their diapause/migration to mate and lay eggs. One study found that 91% of the monarchs tested in Miami had consumed tropical milkweed. (Knight and Brower, 2009). Diapause means that monarchs do not mate for a period of time, as reproduction costs a lot of energy. Instead, monarchs are able to live longer as adult butterflies so that they are able to migrate towards their overwintering locations.

Are monarch populations declining?

                Monarchs are in decline in their overwintering locations which include Mexico and southern California. However, a study published in 2022 shows that monarch populations across the U.S may have actually been increasing about 1.3% each year since the mid 1990’s! (Crossley et al., 2022) One reason why the overwintering populations are declining is because of the parasite OE. It either kills the monarch or makes them weaker and therefore can’t make it to the overwintering location. In Florida, the monarch populations have also been increasing due to the large amount of available non-native tropical milkweed.

Are monarch butterflies endangered?

                Monarchs were declared endangered by the International Union for Conservation of Nature (IUCN). They have not been listed by U.S Fish and Wildlife.

What about pesticides and milkweeds?

                Large box stores and local nurseries carry the non-native tropical milkweed, which often has either topical or systemic pesticides. These pesticides will most definitely kill monarchs. Search for local, native plant nurseries where you can purchase native milkweeds to your area and be sure to ask if they use any pesticides.

Can I just wash my tropical milkweed or treat it with bleach to prevent the OE?

                 Washing your tropical milkweed is not really practical. You might try to be very diligent about washing your milkweed to lower OE amounts but if neighboring properties do not, the high amounts and rates of transmission will continue. Bleach is good at killing many bacteria, fungus, and a few protozoa parasites with enough contact time. But, many protozoal parasite cysts like the form of OE on plants, can be resistant to bleach. Bleach is also readily inactivated when it comes in contact with organic matter and can cause plant damage. Even with all of these possible measures, cleaning tropical milkweed does prevent the other damaging effects of tropical milkweed such as halting migration and spreading invasively to surrounding areas. 

Want to know even more??? 

Dr. Andy Davis discusses the parasite OE: https://www.monarchscience.org/single-post/monarchs-have-a-growing-parasite-problem-and-it-s-not-from-natural-causes

Zoom interview with Dr. Andy Davis and Zoo Miami: https://www.monarchscience.org/single-post/what-to-do-about-monarchs-and-their-parasites-in-florida-a-zoom-conversation-with-miami-zoo-expert

Find out where the parasite OE occurs: https://www.monarchparasites.org/maps

A University of Florida webpage that shows the Florida native milkweeds: https://gardeningsolutions.ifas.ufl.edu/plants/ornamentals/milkweed.html

Relevant Scientific Publications:

Crossley, M., Meehan, T., Moran, M., Glassberg, J., Snyder, W., Davis, A., 2022. Opposing global change drivers counterbalance trends in breeding North American monarch butterflies. Glob. Change Biol. 28, 4726–4735.

Davis, A., 2021. Captive-reared migratory monarchs fly in the wrong direction: a critique of Wilcox et al. Conserv. Physiol. 9.

Davis, A., Smith, F., Ballew, A., 2020. A poor substitute for the real thing: captive-reared monarch butterflies are weaker, paler and have less elongated wings than wild migrants. Biol. Lett. 16. http://dx.doi.org/10.1098/rsbl.2019.0922

Harvey, R., Howell, P., Morgenstern, C., Mazzotti, F., n.d. Native Habitats for Monarch Butterflies in South Florida. University of Florida.

Howard, E., Davis, A., 2015. Investigating Long-Term Changes in the Spring Migration of Monarch Butterflies (Lepidoptera: Nymphalidae) Using 18 Years of Data From Journey North, a Citizen Science Program. Ann. Entomol. Soc. Am. 108, 664–669.

Knight, A., Brower, L., 2009. The Influence of Eastern North American Autumnal Migrant Monarch Butterflies (Danaus plexippus L.) on Continuously Breeding Resident Monarch Populations in Southern Florida. J. Chem. Ecol. 35, 816–823. https://doi.org/10.1007/s10886-009-9655-z

Majewska, A., Altizer, S., 2019. Exposure to Non-Native Tropical Milkweed Promotes Reproductive Development in Migratory Monarch Butterflies. Insects 10.

Majewska1, A., Davis, A., Altizer, S., de Roode, J., 2022. Parasite dynamics in North American monarchs predicted by host density and seasonal migratory culling. J. Anim. Ecol. 91, 780–793.

Oberhauser, K., Nail, K., Altizer, S., 2015. Monarchs in a Changing World : Biology and Conservation of an Iconic Butterfly. Comstock Publishing Associates, Cornell University Press.

Solis-Sosa, R., Semeniuk, C., Larrivee, M., Cox, S., 2022. Investing in monarch conservation: understanding private funding dynamics. Front. Conserv. Sci. 3. https://doi.org/doi: 10.3389/fcosc.2022.903132

Zanden, H., Chaffee, C., Gonzalez-Rodriguez, A., Flockhart, D.T.T., Norris, R., Wayne, M., 2018. Alternate migration strategies of eastern monarch butterflies revealed by stable isotopes. Anim. Migr. 5.