How many monarchs are left
Two counts, done in completely different ways, on two populations that never meet. Between them they are the evidence behind every statement anyone makes about monarch decline, including the ones on this site.
The eastern population
Almost every monarch east of the Rockies spends the winter in a handful of oyamel fir stands in Michoacán and the State of Mexico. They cluster so densely that counting individuals is impossible, so the survey measures something else: the area of forest the clusters cover, in hectares, once each December. It has been done the same way since the winter of 1993, which is what makes it worth anything at all.
Read it carefully and two things stand out. The first is the obvious one: the average across the last ten winters is 2.8 hectares against 8.5 across the first ten, a fall of about 67 percent. The second is how violently it swings year to year. A single bad storm at the overwintering sites, or a hot dry spring in Texas, moves this number more than a decade of habitat work does. Anyone quoting a single winter as evidence of anything is overreaching.
What the number is not is a count of butterflies. Density inside an occupied hectare varies, estimates of how many monarchs that represents range from about ten to more than fifty million per hectare, and the survey deliberately does not make the conversion.
The western population
West of the Rockies monarchs winter in coastal California groves instead, in far smaller aggregations that can genuinely be counted. Volunteers visit several hundred sites over about three weeks around Thanksgiving. This is a real count of individuals, so the numbers cannot be compared with the Mexican hectares in any direct way.
The western series tells a harder story than the eastern one. It has fallen roughly 52 percent comparing decade to decade, and in 2020 it very nearly ended: 1,914 butterflies across the entire wintering range. The rebound in the three years after that was real and surprised everybody, and the 2024 count of 9,119 suggests the rebound did not hold.
Because the western population is so much smaller, its counts are far noisier. A grove missed, or a warm week shifting when butterflies arrive, changes the total by a large fraction.
What both series can and cannot tell you
- They measure winter, not summer. Both count the same generation in the same few weeks. Neither tells you how many monarchs bred in your state.
- They are indices, not censuses. Consistent method over a long period is what gives them value. Neither is a headcount.
- Year-to-year noise is enormous. Weather at three points in the annual cycle can move either number more than habitat can. Trends over a decade mean something; single years mostly do not.
- They cannot be added together. Different populations, different units, different methods.
- They do not tell you why. Milkweed loss, nectar shortage, insecticides, herbicides, disease, drought and forest degradation all plausibly contribute, and separating them is genuinely unresolved.
What follows from all that is fairly plain: the trend is downward in both populations, it is driven by things happening across an entire continent, and the one lever available to an individual is habitat. Find what is native where you live and put some in the ground.
The data
Both series in full, free to reuse. If you are citing monarch decline anywhere, cite these rather than a news story about them.
Eastern population: hectares occupied
| Winter | Hectares occupied | Change on the year before |
|---|---|---|
| 1993–94 | 6.23 | — |
| 1994–95 | 7.81 | +25% |
| 1995–96 | 12.61 | +61% |
| 1996–97 | 18.19 | +44% |
| 1997–98 | 5.77 | -68% |
| 1998–99 | 5.56 | -4% |
| 1999–00 | 9.05 | +63% |
| 2000–01 | 2.83 | -69% |
| 2001–02 | 9.35 | +230% |
| 2002–03 | 7.54 | -19% |
| 2003–04 | 11.12 | +47% |
| 2004–05 | 2.19 | -80% |
| 2005–06 | 5.91 | +170% |
| 2006–07 | 6.87 | +16% |
| 2007–08 | 4.61 | -33% |
| 2008–09 | 5.06 | +10% |
| 2009–10 | 1.92 | -62% |
| 2010–11 | 4.02 | +109% |
| 2011–12 | 2.89 | -28% |
| 2012–13 | 1.19 | -59% |
| 2013–14 | 0.67 | -44% |
| 2014–15 | 1.13 | +69% |
| 2015–16 | 4.01 | +255% |
| 2016–17 | 2.91 | -27% |
| 2017–18 | 2.48 | -15% |
| 2018–19 | 6.05 | +144% |
| 2019–20 | 2.83 | -53% |
| 2020–21 | 2.10 | -26% |
| 2021–22 | 2.84 | +35% |
| 2022–23 | 2.21 | -22% |
| 2023–24 | 0.90 | -59% |
| 2024–25 | 1.79 | +99% |
Western population: butterflies counted
| Year | Butterflies counted | Change on the year before |
|---|---|---|
| 1997 | 1,235,490 | — |
| 1998 | 564,349 | -54% |
| 1999 | 267,574 | -53% |
| 2000 | 394,781 | +48% |
| 2001 | 209,570 | -47% |
| 2002 | 99,353 | -53% |
| 2003 | 209,820 | +111% |
| 2004 | 205,085 | -2% |
| 2005 | 221,058 | +8% |
| 2006 | 86,437 | -61% |
| 2007 | 86,932 | +1% |
| 2008 | 130,317 | +50% |
| 2009 | 58,468 | -55% |
| 2010 | 143,204 | +145% |
| 2011 | 92,798 | -35% |
| 2012 | 144,812 | +56% |
| 2013 | 211,275 | +46% |
| 2014 | 234,731 | +11% |
| 2015 | 292,888 | +25% |
| 2016 | 298,464 | +2% |
| 2017 | 192,668 | -35% |
| 2018 | 27,721 | -86% |
| 2019 | 29,418 | +6% |
| 2020 | 1,914 | -93% |
| 2021 | 247,237 | +12817% |
| 2022 | 335,479 | +36% |
| 2023 | 233,394 | -30% |
| 2024 | 9,119 | -96% |
Both series as JSON, with methods and sources attached.
Sources
- Eastern. WWF Mexico, CONANP and the Monarch Fund annual overwintering survey. Area of oyamel fir occupied by overwintering clusters, surveyed each December. WWF Mexico
- Western. Xerces Society Western Monarch Count. Volunteer counts at California overwintering groves over roughly three weeks around Thanksgiving. westernmonarchcount.org
Figures are transcribed from the published annual reports. Where a season has been revised after first publication, the revised figure is used. Corrections are welcome at contact@milkweedusa.com.
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Milkweed USA. (2026). How many monarchs are left. Retrieved DATE, from https://milkweedusa.com/monarch-population/
"How many monarchs are left." Milkweed USA, 2026, https://milkweedusa.com/monarch-population/. Accessed DATE.
Milkweed USA. "How many monarchs are left." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/monarch-population/.
@misc{milkweedusa_monarchpopulation,
title = {How many monarchs are left},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/monarch-population/},
note = {Accessed DATE}
}