Sacramento Mountains checkerspot butterfly: last known caterpillar has died

May 5, 2026, ABQ BioPark in Albuquerque, New Mexico: The last known caterpillar of the Sacramento Mountains checkerspot butterfly dies—and with it, perhaps, the chance to save an entire butterfly subspecies from extinction. Researchers had hoped that the caterpillar would still transform into an adult butterfly. Then it might have been possible to find a mate in the wild and establish a new generation. But that hope was not fulfilled.

The caterpillar had already hatched at the BioPark in 2022, after researchers captured four wild butterflies to establish a conservation breeding programme. More than 160 caterpillars resulted from these animals. In the end, only one remained. It lived for three years without pupating. When it finally stopped eating, the team placed it into winter dormancy. In spring it was supposed to be warmed up again, but after several days of careful observation it became clear: the caterpillar was dead.

Officially, the Sacramento Mountains checkerspot (Euphydryas anicia cloudcrofti) is therefore not yet considered extinct, but its situation is critical. Since the Forest Service began formal surveys in 1999, the population has declined sharply. By 2012, the subspecies occupied only about half as many monitored sites as before; after that, the decline continued. The Forest Service therefore considers it probably the most endangered butterfly in the United States.

Since 2022, the butterfly has not been reliably confirmed in the wild. An as yet undiscovered remnant population is still possible, which is why researchers plan to search for it again in 2026. The body of the dead caterpillar will now be stored frozen at the Museum of Southwestern Biology at the University of New Mexico so that it can be used for future genome research.

A life across just a few square kilometres

The Sacramento Mountains checkerspot butterfly is considered a subspecies of the more widespread Anicia checkerspot (Euphydryas anicia). How large its original range once was is not known. Systematic surveys across the entire known range were carried out comparatively late: between 1996 and 1997, researchers first conducted a more comprehensive investigation of where the subspecies still occurred at all.

This revealed just how narrowly limited its habitat is. The butterflies were found within an area of only about 82 square kilometres. Yet even this small area is not entirely suitable habitat. In fact, the usable habitat within this area covers only around 5.2 square kilometres. The Sacramento Mountains checkerspot butterfly therefore does not inhabit a continuous, large-scale range, but an extremely small habitat mosaic made up of a few suitable mountain meadows.

Its known occurrence is restricted to the Sacramento Mountains in southern New Mexico, more precisely to high-elevation mountain and subalpine meadows around the town of Cloudcroft in the Lincoln National Forest. The U.S. Fish and Wildlife Service (USFWS) describes the subspecies as inhabiting meadows at elevations between about 2,380 and 2,740 metres.

This close dependence on a few suitable areas makes the butterfly especially vulnerable. If such meadows are affected by climate change, altered fire regimes, overgrazing, invasive plants or recreation, there are hardly any alternative areas. What for a widespread species would merely mean the loss of part of its habitat can be existentially threatening for a locally restricted subspecies.

Many butterflies depend on specific plants during their caterpillar stage. Their caterpillars do not eat just any leaves, but often only a few suitable host plants. For the Sacramento Mountains checkerspot butterfly, the New Mexico penstemon (Penstemon neomexicanus) is the only known caterpillar food plant—a violet-flowering plant from the plantain family. The butterflies lay their eggs on this plant; the caterpillars then use it as food and shelter.

The adult butterflies, too, are tied to the plant communities of their mountain meadows. Their preferred nectar source is considered to be orange sneezeweed (Hymenoxys hoopsii), a native perennial plant with yellow-orange flowers. The subspecies’ survival therefore depends not only on open mountain meadows, but also on the right plants being available at the right time. What was a successful specialization for a long time can become a risk in a rapidly changing environment.

The “elevator to extinction”

Species that live at higher elevations are considered especially vulnerable under climate change. This also applies to the Sacramento Mountains checkerspot butterfly. As temperatures rise, many species can theoretically shift into cooler regions, for example farther north or to higher elevations. But on a mountain, this escape route is limited: at some point there is no higher habitat left. It is, so to speak, an “elevator to extinction”: species move farther and farther upslope until the mountain ends. For the Sacramento Mountains checkerspot butterfly, this risk is very high, because its few suitable mountain meadows are already at higher elevations.

In addition, climate change does not only mean higher temperatures. It also changes precipitation, dry periods, plant growth, fire regimes and seasonal timing. For butterflies, this can lead to problems. Their development is closely linked to specific plants and climatic conditions. If caterpillars become active at a time when their food plants are not yet available or have already dried out, an ecological mismatch occurs. The timing between insect and plant falls out of sync.

The USFWS does not name a single trigger for the decline, but several interconnected pressures: degraded habitats, unsuitable grazing, recreation, climate change, altered fire regimes and invasive and non-native plants. For small, isolated remnant populations, such a combination can become existentially threatening: one unfavourable weather year, a fire nearby, a failed flowering season or an extremely dry summer can then be enough to weaken the population further.

Late protection for the Sacramento Mountains checkerspot

As early as 1999, the Center for Biological Diversity, a nonprofit conservation organization, petitioned for the butterfly subspecies to be placed under the protection of the U.S. Endangered Species Act. At the time, the USFWS concluded that listing might be warranted, but in reality it took more than two decades before the checkerspot subspecies received this protection.

Only in 2023 was the subspecies officially added to the higher of the two central threat categories: endangered—a classification for species that are in danger of extinction throughout all or a significant portion of their range. In the same year, the agency also proposed designating around 662 hectares as critical habitat.

For the Sacramento Mountains checkerspot butterfly, this protection may have come too late. For species with small populations, it is often not enough to act only when just a few individuals are left. Conservation breeding, habitat restoration and monitoring take time. They are much more promising while several stable subpopulations still exist and enough genetic diversity remains.

An isolated case—and yet part of a larger pattern

The fate of the Sacramento Mountains checkerspot butterfly stands for a larger pattern: many insect species do not disappear suddenly, but gradually and often unnoticed for a long time.

A 2025 study on butterflies in the USA showed that the total number of recorded individuals across 554 species declined by 22% between 2000 and 2020. Twenty-two species even lost more than 90% of their populations. This is also worrying because butterflies are among the most conspicuous and best-monitored insects. Similar developments could more easily go unnoticed in less well-recorded groups such as beetles, wild bees or flies.

The decline of butterflies is not a purely North American phenomenon. Declines have also been recorded in Europe and Germany. The Red List of Butterflies and Burnet Moths for Germany found in 2025 that 55% of native species are threatened with population decline or already extinct. And the European Red List of Butterflies also showed a clear deterioration since 2010; almost one in three species is threatened or shows declining populations.

The causes are usually varied. Alongside global warming, the central drivers are above all habitat loss, fragmentation, intensive land use and pesticides. When species-rich meadows, wetlands or structurally rich forest edges disappear, many butterflies lose their breeding and feeding areas. Insecticides can harm animals directly; herbicides often act indirectly by reducing wild plants and thus caterpillar food plants and nectar sources.

Between hope and loss

The death of the caterpillar may not mean the end of the subspecies. But with it, the last known opportunity to continue conservation breeding was lost. Whether a small remnant population still survives somewhere remains open.

The researchers are not giving up the search yet. Quin Baine of the New Mexico BioPark Society, one of the scientists responsible for caring for the caterpillar, told the New York Times that she had still seen some intact habitats last year. That gives hope that the subspecies still exists. At the same time, she is worried about the early heat and a nearby fire this year.

Extinction therefore does not begin only with the last confirmed individual, but much earlier: when habitats shrink, populations become isolated, food plants disappear, seasonal processes fall out of sync, protective measures take effect too late and monitoring gaps conceal declines.

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Sources

• Center for Biological Diversity. (n. d.). Sacramento Mountains checkerspot butterfly. https://www.biologicaldiversity.org/species/invertebrates/Sacramento_Mountains_checkerspot_butterfly/index.html
• Einhorn, C. (2026, May 21). A very lonely caterpillar, possibly the last of its kind, has died. The New York Times.
  https://www.nytimes.com/2026/05/21/climate/a-very-lonely-caterpillar-the-sacramento-mountains-checkerspot-has-died.html
• U.S. Fish and Wildlife Service. (n. d.). Sacramento Mountains checkerspot butterfly (Euphydryas anicia cloudcrofti). https://www.fws.gov/species/sacramento-mountains-checkerspot-butterfly-euphydryas-anicia-cloudcrofti
• U.S. Fish and Wildlife Service. (2025, September 23). Draft recovery plan for Sacramento Mountains checkerspot butterfly available. https://www.fws.gov/press-release/2025-09/draft-recovery-plan-sacramento-mountains-checkerspot-butterfly-available