June is the month of the Monarch Butterfly

Monarch Butterfly, Danaus plexippus and Milkweed, Asclepias spp.

Our pollinator blog posts seek to highlight the amazing qualities – “super powers”- of the tiny creatures that support life on Earth.  The Monarch butterfly’s super power is its amazing 2,500+ mile migration from the northern US and southern Canada all the way to the pine forests of Michoacan, Mexico.  This animal, weighing half a gram, goes on an epic journey, navigating storms, loss of resources, predators, and disease.  How and why this migration occurs is still being studied, but scientists believe that Monarchs use a combination of the sun, polarized light waves, and a magnetic compass to guide them. (Note: Monarchs living west of the Rocky Mountains migrate to sites in Southern California.)

One new study examines the Monarch’s wings in an effort to understand how these tiny animals can fly so far.

Migrating monarchs soar at heights of up to 1,200 feet. As sunlight hits those wings, it heats them up, but unevenly. Black areas get hotter, while white areas stay cooler. The scientists believe that when these forces are alternated, as they are with a monarch’s white spots set against black bands on the wings’ edges, it seems to create micro-vortices of air that reduce drag—making flight more efficient.


The Monarch butterfly’s life cycle and its migration are related.  Monarch butterflies who have been overwintering in Mexico begin to fly northward in mid -March, when temperatures start to warm to 50 degrees or more.  This generation stops in northern Mexico and Texas to lay their eggs.  It takes 4 generations to make it all the way to Canada.  (https://www.fs.usda.gov/wildflowers/pollinators/).

Females seek out nectar plants like Echinacea purpurea and goldenrods, among others, for energy, and milkweeds on which to lay their eggs.  Monarch caterpillars only eat milkweed, so adult females lay their eggs on the undersides of milkweed leaves.  A single Monarch butterfly can lay 300-500 eggs in a 2-4 week period.  The eggs hatch in just 3-5 days.

A Monarch caterpillar grows almost 2,000 times its birth size over the course of about 2 weeks of constant feeding and has to shed its skin 5 times to accommodate the increased mass.  When it is ready for metamorphosis, it will crawl away from the milkweed to find a safe location to “hang out.”  It spins a silk mat to hang onto and hangs upside down in a J-shape, shedding its skin for the last time and forming the chrysalis around it.  This stage lasts about 8-14 days.  When the fully-formed adult butterfly emerges, it pumps fluid from its abdomen to its wings and gently flaps them to dry them out.  Then, it is free to fly and forage and move northward.

As with many pollinators, Danaus plexippus numbers are declining at a rapid rate.




Since milkweed is the only host plant for Monarch caterpillars, protecting milkweed is essential to the survival of the species.  Check this guide for planting tips: https://www.xerces.org/milkweed-faq#2

Milkweed comes from the genus Asclepias, which is derived from the name Asklepios, the Greek god of medicine and healing. American Indians and settlers used the roots of this plant for treating respiratory illnesses and other ailments.  Asclepias consists of 130 species. Of these, 11 varieties are native or naturalized in Pennsylvania. The three most common species in our region are common milkweed (Asclepias syriaca), butterflyweed (Asclepias tuberosa), and swamp milkweed (Asclepias incarnata).


You can help Monarch butterfly conservation efforts in many ways:

  1. Plant native flowering plants in your yard as nectar resources.
  2. Seek out plants free of systemic pesticides.  Ask your nursery for pesticide free plants.*
  3. Plant milkweed as hosts for caterpillars.
  4. Join a citizen science group that monitors Monarch populations.
  • Journey North: This website provides information on tagging and monitoring monarch butterflies as they migrate in the eastern U.S.
  • Monarch Watch.
  • Southwest Monarch Study: The Southwest Monarch Study studies the migration patterns of monarch butterflies in Arizona. Their activities include tagging monarchs, monitoring milkweed populations, and searching for habitats that attract and support monarchs. People of all ages are welcome to participate. Southwest Monarch Study also provides educational programs to raise monarch awareness.
  • The Vanessa Migration Project: This website allows interested indiviuals to help monitor the migration of Painted lady butterflies.
  • North American Butterfly Monitoring Network: A network of volunteer-based monitoring programs throughout North America that collect butterfly abundance and distribution data.

*Some pesticide use in the growing process is common and may not be able to be avoided.  Neonicitinoids are particularly lethal, though, and should be avoided.  Inquiring about the use of pesticides will alert your nursery -and the grow sources they use- that you are aware and concerned for the safety of all pollinators.  Educate yourself on the practices of your grower and on the products they use.

Check out next month’s blog post on the skipper moth!

For further information: