Documenting milkweed (Asclepias spp.) and monarch distribution across the western U.S.

During the spring and summer, monarchs breed across the continental United States and parts of Southern Canada, and yet very little is known about where and when monarchs breed west of the Rocky Mountains. The Xerces Society and others are working to change this situation, and we could use your help!

Monarch butterflies face many threats including the loss of breeding habitat due to the decline of native milkweeds (Asclepias spp.), which monarch caterpillars rely on for food. In collaboration with our partners we are gathering information about the location of monarchs and milkweed stands in the eleven western states: Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. If you know where milkweed grows or have observed breeding or migrating monarchs, please contribute your observations to our growing database!

In hopes of collecting as much data as possible we’ve developed several options for reporting milkweed and monarch observations. You can decide which tool will suit your reporting and observation needs. See below for a brief description of each tool. In addition, we have created guides to the native milkweeds of California, Nevada, Oregon, Washington, and the Great Basin to help you identify milkweeds in your region. You can access these guides as well as other resources on this webpage.

The data collected from these efforts is being used to help the many agencies and organizations engaged in monarch conservation. This includes understanding where and when monarchs breed, as well as planning where planting milkweed and nectar plants would be most effective. You can access and download the database (through 2015) by visiting . The data has also been used to develop a habitat suitability model for monarchs through our partnership with the Pacific Region of the U.S. Fish and Wildlife Service (USFWS). The more data collected, the more accurate this model will be to help identify areas where milkweed plantings (and monarchs) will flourish. Thanks for supporting monarch conservation! Contact with any questions.

Please submit all new observations by October 31st to or through the formats below for inclusion in habitat suitability modeling during winter 2016-2017. We appreciate your contribution to the project.


Report Your Observations Using One of These Tools:


Online SurveyFill out this brief online survey to report milkweed and monarch observations across the West. This tool is great for reporting incidental sightings and ideal for citizen scientists.

Excel WorkbookIf you regularly conduct milkweed and/or monarch surveys for your job and have more detailed information download this Excel workbook and user guide.

data sheet*Updated April 5th, 2016* Download and print a General Observer Data Sheet, a milkweed and/or a monarch data sheet, and our definitions guide to collect data in the field. Afterwards, return to this page and enter data into either online survey or Excel workbook

Monarch SOS App*Now Available* Use the Monarch SOS iPhone App to access monarch resources across the country. Visit the Xerces page in the App to report milkweed and monarch observations with your iPhone. An Android version of this app is forthcoming.

Western Milkweeds and Monarchs Map

Click the image below to view our in-progress Western Milkweed and Monarch Breeding Map, which is based on responses to our online milkweed survey in addition to the published literature, unpublished reports, online herbaria, and knowledgeable researchers and citizen scientists. Click here for a full list of data providers and references. Click here for results from the first iteration of the Western Milkweed and Monarch Habitat Suitability Model based on data collected in 2015. This model will continue to be refined as additional data becomes available.

western milkweed and breeding_updated_may2016

Milkweed Guides

A series of regional guides to the native milkweeds of North America, developed in cooperation with the USDA Natural Resources Conservation Service:

California Native Milkweeds Great Basin Native Milkweeds Nevada Common Milkweeds


Oregon Native Milkweeds Washington Native Milkweeds Desert Southwest Native Milkweeds

Other Resources

University of Minnesota’s Monarch Larva Monitoring Project has images of monarch caterpillars at numerous stages of development.

Journey North has photos of adult monarch butterflies.

Have a question about milkweed? Check out our Milkweed FAQs.

Read more about the North American monarch migration here.

Read about how Xerces is working to restore monarch breeding habitat by increasing the availability of native milkweed seed.

Milkweeds and Monarchs in the Western U.S. – This guide outlines how land managers can join existing efforts to help western monarchs by identifying and reporting milkweed stands and monarch breeding occurrences on their lands.

Icons courtesy of The Noun Project: Computer icon designed by Martin Vanco. Excel file icon designed by Alice Cerconi. iPhone icon designed by Mr Robot. Clipboard icon designed by Greg Beck. Monarch butterfly on showy milkweed by Edward Lisowski.



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Program Features
Program Highlights
  • • The Xerces Society has awarded two $3,750 Joan M. DeWind awards for research into lepidoptera conservation
  • Butterfly-a-thon pledges raise $30 per species that Bob Pyle observes for butterfly conservation work
Additional Information