CEC hero image, a photo of Array


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.

Join this year’s International Monarch Monitoring Blitz from 26 July to 4 August 2024!

To take part in the Blitz, please share your observations through one of the participating community science programs below:



United States:

Monarch Blitz

Highlights from the 2023 International Monarch Monitoring Blitz:

We are celebrating seven years of Community Science with very encouraging results from this year’s Monarch Blitz! Here are some highlights from the 2023 trinational effort:

  • 3,998 observations
  • 1,789 participants from 76 states and provinces
  • 13,222 monarchs observed
  • 40,616 examined milkweeds

See our full statement, and learn how you can download Blitz Data, here.

Summary of the last seven editions (2017-2023) of the International Monarch Monitoring Blitz, a community science initiative:

  • 9,122 participants across Canada, Mexico, and the United States
  • 20,205 observations
  • 322,253 milkweed plants monitored
  • 112,803 monarchs observed
  • 42,846 eggs
  • 37,582 caterpillars
  • 2,245 chrysalises

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.


The 2023 International Monarch Monitoring Blitz was a great example of community science participation and collaboration across North America. The results have also been showcased through the CEC’s MapMonday initiative which highlights North American geospatial data, especially in relation to the CEC’s North American Environmental Atlas.

Monarch Blitz 2023 Participation Map

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.

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!

Logo Mission Monarch

Mission Monarch


Participating Partner Logo



Logo Western Monarch Milkweed Mapper

Western Monarch Milkweed Mapper

Western United States

Logo - Journey North

Journey North

North America

Monarch Larva Monitoring Project

North America

Correo Real


Canadian Wildlife Federation + iNaturalist Canada



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

Participating Partner Logo
Participating Partner Logo
Logo Monarch Joint Venture
Xerces Society for Invertebrate Conservation
Participating Partner Logo
Environment and Climate Change Canada
Participating Partner Logo - USFWS
agency profauna
Canadian Wildlife Federation


Georgina O’Farrill
Head of Unit, Outreach and Partnerships
(514) 350-4336