Monarch Butterfly
Fast Facts
Migrate south each Fall to overwintering grounds in Mexico.
Populations have been declining mainly due to habitat loss and the use of herbicides.
Listed as “Endangered” by the IUCN and is a candidate for listing under the Endangered Species Act.
You can help them by planting milkweed in your yard and by encouraging your neighbors to as well.
Where: Fields, meadows, and gardens containing wildflowers; especially those with milkweed plants
Size: 3.5-4 inch wingspan; weigh less than a paperclip
Found in the Northeast throughout the summer and into early-Fall.
Feed on nectar from a wide range of wildflowers.
Lay eggs on, and caterpillars develop on, milkweed plants.
Creature Feature
Photo by @iowanaturalist
Introduction
Monarch Butterflies are probably the most recognizable of all butterflies in the Northeast. Their large size and unique orange, black, and white patterns make them easy to spot.
Map from monarchwatch.org
There are actually two distinct populations of Monarch Butterflies in North America. One population is west of the Rockies, and the other is east of the Rockies.
Photo by @coeli_ingold
Monarch Migration
Every spring, Monarch Butterflies leave their overwintering locations in Mexico (more on this later). They migrate north to breed in the U.S. and southern Canada.
Image by U.S. National Park Service
Monarchs arrive here in the Northeast (and SE Canada) in mid-to-late summer. Those that reach the Northeast are mostly 3rd-generation individuals of the year. They are the "great-grandchildren" of the Monarch Butterflies that overwintered in Mexico.
Fall migration map (by www.monarchmigration.org)
The Monarch Butterflies that grow from eggs laid on Milkweed in late-summer in the Northeast are the final generation of the year. It is these individuals that will then make the final leg of the annual circuit. They fly some ~3,000 miles to the overwintering grounds in Mexico. These are the ones who will start the northward migration next spring.
Photo by Adam Jones
Winter Refuge
Most Monarch Butterflies that survive their long migration overwinter in a small area in central Mexico. They spend the entire winter there in high elevation (1.5-2 miles above sea level) fir forests. They typically arrive there in early-November and stay until March.
Photo by Carlos Adampol
There is not much food available to them there. They survive the winter mostly on energy stored during their fall migration.
Photo by Adam Jones
They conserve energy in winter by spending most of their time perched in branches of the fir trees. They often perch in large clusters. There can be as many as 15,000 Monarch Butterflies on a single tree branch. Perching in clusters also helps them keep warm.
Photo by U.S. Fish and Wildlife Service
Due to their high elevation in the mountains, it sometimes gets below freezing and rarely it even snows where they overwinter. As long as they don’t experience heavy snowfall events, most will survive the winter.
For a long time it was a mystery where Monarch Butterflies spent their winters. A Canadian biologist, Dr. Fred Urquhart solved this mystery in 1975. In 1976, National Geographic celebrated this momentous discovery on its cover.
Photo by @birdsnbuddies
Monarchs In Decline
Monarch Butterfly populations have been declining over the past two decades. Two major reasons are loss of habitat and effects of herbicides.
Image by Lorie Shaull
Monarchs need milkweed to lay their eggs and for their caterpillars to develop on. Milkweed has been declining in North America due to: 1) widespread herbicide use, and 2) the conversion of grasslands to agriculture and development.
Monarch caterpillars feeding on milkweed (by @belawi.photography)
Monarch Butterflies only lay their eggs on milkweed plants. They do this because their caterpillars get toxins from eating milkweed leaves. This provides protection from predators for the caterpillars and the adult butterflies.
Monarch Butterfly on a clover flower (by @berkshire_wildlife_photography)
In 2022, the IUCN listed the Monarch Butterfly as "Endangered." The Monarch Butterfly is also a candidate for listing under the Endangered Species Act by the U.S. Fish and Wildlife Service.
Avoiding mowing milkweed plants (by Oregon Dept. of Transportation)
Fortunately, many organizations are working to protect the Monarch Butterfly. These include Federal and State agencies, and many NGOs ("non-governmental organizations").
Ranger and students at a milkweed plant (by U.S. National Park Service)
Most of the conservation work is on habitat. It aims to conserve and create habitats. It also seeks to reduce herbicide and pesticide use. Education is also a big part of the equation. And you can become a part of the solution by taking some of the steps listed below.
Observations by Month
The plots above show the number of observations of Monarch Butterflies for each month for each Northeast State through 2023 (from iNaturalist). You’ll note a general trend of increasing from June - August (as they migrate into the Northeast and reproduce), followed by a rather steep drop in observations in September and October (as they leave on their southward migration to overwintering grounds).
Plant milkweed in your yard: Learn more here
Plant wildflower gardens/meadows: Convert part of your yard to native wildflower meadows; among many other benefits of doing this, this creates a natural food source for Monarch Butterflies (and for lots of other butterflies too!).
Don’t use herbicides or pesticides