International Monarch Monitoring Blitz

The International Monarch Monitoring Blitz invites community scientists from across North America to come together with the shared goal of helping to protect and conserve the beloved and emblematic monarch butterfly. Data collected by volunteers each year support trinational efforts to better understand the monarch butterfly’s breeding productivity, range, and timing in North America.

This year’s Blitz takes place between 29 July and 7 August.

Illustration of the monarch butterfly lifecycle including an egg, chrysalid, caterpillar, and adult butterfly on different parts of a milkweed plant

Illustration courtesy of Biodiversity Heritage Library.

Which Community Science Program is Right for You?

Participating in the Monarch Blitz requires you to simply track your observations of the monarch butterfly. If you spot a monarch egg, caterpillar, and/or adult or milkweed, no matter where you are near the end of July or beginning of August, you’re encouraged to share your observation with one of several Community Science programs displayed below.

Curious which program is right for you?

Have a look through the programs below to find one that works for you!


Mission Monarch



Western United States

Western Monarch Milkweed Mapper

North America

Journey North

North America

Monarch Larva Monitoring Project

Why Community Science?

The information collected by North American community science observers helps researchers identify priority areas for monarch conservation actions. Thanks to this engaged community of observers, monarch researchers will soon be able to analyze trends in summer breeding population sizes. All partner organizations have agreed to share volunteer-collected data to a central data repository. In this way, anyone can consult and download Blitz data by visiting the TRINATIONAL MONARCH KNOWLEDGE NETWORK.

Two community scientists seated in a field. One writes down observations as another examines a milkweed plant
A community scientist crouching down to look for signs of the monarch butterfly on a milkweed plant

Volunteer participation and the engagement of volunteers grows year after year, and experts believe that the Monarch Blitz database, made up almost exclusively of observations shared by volunteer community scientists, will achieve the original objective set for the Monarch Blitz by the Trinational Monarch Conservation Science Partnership: a rigorous estimation of the size of the summer breeding population, similar to what is done with the overwintering populations in central Mexico and coastal California.

Furthermore, researchers are interested in assessing population trends. Reporting the number of caterpillars and the number of milkweed stems can allow the calculation of a caterpillar-to-milkweed ratio. Researchers can then use this ratio to estimate the size of the population of monarchs that are migrating to Mexico at this time of year.

Summary of the last five editions of the International Monarch Monitoring Blitz, a community science initiative:

  • 4,635 participants across Canada, Mexico, and the United States
  • 10,219 observations
  • 212,790 milkweed plants monitored
  • 80,383 monarchs observed
  • 33,358 eggs
  • 27,728 caterpillars
  • 1,661 chrysalises
  • 16,672 butterflies
A map of North America displaying five years of Monarch Blitz observations

Click to enlarge

Facts about the Monarch

  • Monarch butterflies weigh less than a gram.
  • There are two recognized migratory routes in North America: Eastern and Western.
  • Migration covers 3,000-5,000 km (2,000 to 3,000 miles) and spans three countries.
  • The Eastern migratory population has declined by more than 80% in 20 years.
  • The Western population has declined by 99% since the 1980s.
  • Everyone can help the monarch butterfly by participating in community science, creating monarch-friendly habitats, and spreading the word about the monarchs’ status and importance as a pollinator.
A monarch butterfly sitting on top of a pink flower.

Image courtesy of Amy Evoniuk Photography.

2021 Observations

What do the colors mean?

  • Light grey: A low number of observations of either monarch or milkweed
  • Yellow: A high number of monarch observations
  • Blue: A high number of milkweed observations
  • Red: A high number of both monarch and milkweed observations
A map of North American displaying the concentration of milkweed and monarch observations collected in the 2021 Monarch Blitz

Click to enlarge


The Blitz is organized by the Trinational Monarch Conservation Science Partnership, a collaboration of organizations, including:

Monarch Blitz Partner Agency
Monarch Blitz Partner Agency
Monarch Blitz Partner Agency
Monarch Blitz Partner Agency
Monarch Blitz Partner Agency
Monarch Blitz Partner Agency
Monarch Blitz Partner Agency


Bhan Gatkuoth
Coordinator, Diverse and Inclusive Outreach and Engagement
(514) 350-4324