Monarch Butterfly

Danaus plexippus
Monarch 520x289

The monarch butterfly (Danaus plexippus) is perhaps the most well-known butterfly species in North America. This is due in part to its easily recognized orange, black, and white wing pattern. But perhaps monarchs are best known for their lengthy migrations and consistent population declines over the past two decades [1]. Recent population declines led several nonprofit organizations to petition the United States Fish & Wildlife Service (USFWS) in 2014 to protect the monarch butterfly under the Endangered Species Act (ESA) [2]. Many factors have been suggested to have influenced the monarch’s decline such as degradation of overwintering forests, loss of breeding habitat, loss of nectar plants, and loss of milkweed (Asclepias spp.) [4,5,6,7,8].

Because of the monarch’s declining populations and numerous identified threats, a Presidential Proclamation was issued in 2014 directing federal agencies to protect monarch butterflies and other pollinators [9]. The USFWS meets this request by conserving and managing protected lands through the National Wildlife Refuge System (NWRS). Coastal refuges, such as Anahuac National Wildlife Refuge (NWR), provide essential habitat for ensuring the viability of at risk species like the monarch butterfly. Anahuac NWR’s specific location plays a vital role in supporting the lengthy monarch migrations. Monarchs in North America are divided into two populations, the western population (west of the Rocky Mountains) that makes a truncated fall migration to California, and the eastern population (east of the Rocky Mountains) that makes an extended fall migration to overwintering sites in the mountains of Mexico [10,11]. Some monarchs in the Eastern population migrate up to 2667 miles (4,293 km) from their breeding areas in Canada to Mexico [8,11]. During this extensive fall migration, many monarchs use an identified coastal flyway that brings them through Anahuac NWR, with peak migrations during middle to late October [12]. Exhausted and in need of energy, Anahuac NWR provides much needed nectar plants to help fuel the rest of the monarch’s journey southward. Anahuac NWR’s diverse coastal marshes and prairies are home to numerous native fall-blooming plants, such as Missouri ironweed (Vernonia missurica), blue mistflower (Conoclinium coelestinum), blazing star (Liatris spp.), and goldenrod (Solidago spp.) that are known monarch nectar sources [13,14]. Salt tolerant Eastern baccharis (Baccharis halimifolia) and marsh elder (Iva frutescens) are not known monarch nectar sources, but provide valuable roosting habitat along Galveston Bay during cold temperatures and strong winds where trees are scarce on the refuge.

After monarchs have overwintered in the high altitude oyamel fir (Abies religiosa) forests of Mexico, they mate and begin their journey back northward in March [4,8]. Female monarchs seek out milkweed for ovipositing as lipid sources continue to dwindle [8]. Conceivably more important than nectar flowers at this stage of the remigration, several milkweed species are present throughout Anahuac NWR, such as green antelopehorn (Asclepias viridis), and offer a place for the next generation of monarchs to grow. Interestingly, monarch researchers suggest that it takes two to three generations of monarchs to make it back to their summer breeding grounds before the next fall migration ensues [15]. Milkweed also provides monarchs with chemical protection in the form of cardenolides that are sequestered to protect against potential predators, in addition to being the only larval food source, illustrating the importance of milkweed along the remigration route [16,17]. Anahuac NWR hosts many species of spring blooming plants that monarchs nectar from such as lantana (Lantana spp.), sunflower (Helianthus spp.) and common buttonbush (Cephalanthus occidentalis) [13,14]. Surprisingly, these spring blooming plants may be most important to the successive generations of developing monarchs as it is unknown whether the remigrating population of monarchs nectar on their northward journey [8].  

Anahuac NWR supports monarch populations predominately by fighting two of the suggested causes of monarch decline, loss of nectar sources and loss of larval host plants. But other refuges along the Gulf Coast such as McFaddin NWR, Moody NWR, and Texas Point NWR also support monarch conservation by encouraging native nectar plants and milkweeds. Together NWRs continue to conserve and manage wildlife and the habitats in which we all depend on.  


Literature Cited

1. Vidal, O. and E. Rendon-Salinas. 2014. Dynamics and trends of overwintering colonies of the monarchs butterfly in Mexico. Biological Conservation 180:165-175.

2. USFWS. 2017. Assessing the status of the monarch butterfly. Accessed on 10Nov2017.

3. Pleasants, J.M. and K.S. Oberhauser. 2013. Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population. Insect Conservation and Diversity 6:135-144.

4. Brower, L.P., G. Castilleja, A. Peralta, J. Lopez-Garcia, L. Bojorquez-Tapia, S. Diaz, D. Melgarejo, and M. Missrie. 2002. Quantitative changes in forest quality in a principal overwintering area of the monarch butterfly in Mexico, 1971-1999. Conservation Biology 16:346-359.  

5. Brower, L.P., O.R. Taylor, E.H. Williams, D.A. Slayback, R.R. Zubieta, and M. Isabel. 2012. Decline of monarch butterflies overwintering in Mexico: is the migratory phenomenon at risk? Insect Conservation and Diversity 5:95-100.

6. Flockhart, D.T., J.B. Pichancourt, D.R. Norris, and T.G. Martin. 2015. Unravelling the annual cycle in migratory animal: breeding-season habitat loss drives population declines of monarch butterflies. Journal of Animal Ecology 84:155-165.

7. Pleasants, J.M. and K. Oberhauser. 2013. Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population. Insect Conservation and Diversity 6: 135-144. 

8. Brower, L.P., L.S. Fink, and P. Walford. 2006. Fueling the fall migration of the monarch butterfly. Integrative and Comparative Biology 46: 1123-1142.

9. White House. 2014. Presidential Proclamation. Accessed 14Nov2017.

10. Monarch Watch. 2010. Two-way monarch migration map. Accessed on 12Nov2017.

11. Brower, L.P. 1995. Understanding and misunderstanding the migration of the monarch butterfly (Nymphalidae) in North America: 1957-1995. Journal of the Lepidopterists’ Society 49:304-385.

12. Calvert, W.H. and M. Wagner. 1999. Patterns in the monarch butterfly migration through Texas 1993 to 1995. In Jurgen Hoth, Leticia Merino, Karen Oberhauser, Irene Pisanty, Steven Price, and Tara Wilkinson, editors. 1997 North American conference on the monarch butterfly. Commission for Environmental Cooperation. p 119-125.

13. Xerces Society. 2017. Monarch nectar plant guide: southern plains.  Accessed on 10Nov2017.

14. USDA, NRCS. 2017. Monarch nectar plant list for the southern plains. Accessed on 12Nov2017.

15. Malcolm, S.B., B.J. Cockrell, and L.P. Brower. 1993. Spring recolonization of eastern North America by the monarch butterfly: successive brood or single sweep migration? In S.B. Malcolm and M.P. Zalucki, editors. Biology and conservation of the monarch butterfly. Natural History Museum of Los Angeles County. p 253-267.

16. Malcolm, S.B. and Brower, L.P. 1989. Evolutionary and ecological implications of cardenolide sequestration in the monarch butterfly. Experientia 45: 284-295.

17. Malcolm, S.B. 1994. Milkweeds, monarch butterflies and the ecological significance of cardenolides. Chemoecology 5:101-117. 

Facts About Monarch Butterfly

Description- 3.5 - 4 inches; orange, black, and white wings

Larval Plants- milkweed (Asclepias spp.)

Nectar Plants- Missouri ironweed (Vernonia missurica), blue mistflower (Conoclinium coelestinum), blazing star (Liatris spp.), goldenrod (Solidago spp.), lantana (Lantana spp.), sunflower (Helianthus spp.) and common buttonbush (Cephalanthus occidentalis)

Migration Length- up to 2,667 miles

Peak Migration Time- mid to late October on Anahuac National Wildlife Refuge