Reproductive pair (amplexus) of the Milpe Robber Frog photographed at night on a leaf in the tropical forest of the Ecuadorian Chocó. Credit: Santiago R. Ron

Pristimantis milpe is a common and widespread species that was mistaken for another species for more than a century.

For more than a century, a common frog living across the forests of western Ecuador and southern Colombia was hiding in plain sight under the wrong scientific name. Researchers at the Pontificia Universidad Católica del Ecuador have now formally described Pristimantis milpe as a distinct species after revisiting specimens collected in Ecuador during the 19th century and stored at the Natural History Museum in London.

What makes the discovery unusual is how familiar the frog already was. Newly described species are often rare or confined to small areas, but Pristimantis milpe is abundant, widespread, and readily detected by its nighttime call. Its known range covers more than 67,000 square kilometers of the Chocó forests in western Ecuador and southern Colombia, extending from sea level to elevations of 1,200 meters.

The formal description appears in the international journal ZooKeys, which specializes in biodiversity and taxonomy research.

The Milpe Robber Frog lives in a wide variety of habitats, from parks in urban areas to primary forests. The individual in the photo comes from the Río Ayampe Reserve in the Manabí province. Credit: Diego Paucar

Museum specimens resolved a century-old error

The key to identifying Pristimantis milpe came from historical amphibian specimens held in the collections of the Natural History Museum in London (NHM).

Santiago Ron, a researcher at PUCE and lead author of the study, traveled to England to investigate the taxonomic confusion that had persisted for more than 100 years. He examined the original specimens, known as “types,” that were collected in Ecuador during the 19th century and preserved in the museum ever since.

Amphibiologist Santiago Ron, the leading author of the study. Credit: Santiago R. Ron

By comparing those historical specimens with frogs living today in the Ecuadorian Chocó, the researchers found that the old material had been incorrectly assigned to another species. As a result, a common frog that scientists had encountered for decades remained without its own scientific name.

“That such a common species has gone unnoticed under the wrong name for decades highlights the importance of correctly connecting scientific names with living populations in nature,” notes Jhael Ortega, a PhD student at Virginia Tech and one of the study authors.

Calls and color distinguish the species

The Milpe Robber Frog (Cutín de Milpe) is active at night. Males typically call from leaves on shrubs and bromeliads several meters above the forest floor, producing a loud, distinctive vocalization resembling a “click.”

The Ecuadorian Chocó forest is home to more than 250 species of amphibians, including the Milpe Robber Frog, Pristimantis milpe. Credit: Santiago R. Ron

Females and males also differ noticeably in appearance. Females have distinctive coloring on the groin and thighs, with orange or light blue tones marked by black spots, while males tend to display more uniform coloration.

The frog occurs in the forests of the Ecuadorian Chocó and southern Colombia, a region considered especially important for biodiversity conservation.

Historical collections still reshape biodiversity

The discovery underscores the continuing scientific importance of natural history collections. Specimens preserved for generations can allow researchers to revisit classifications, compare physical characteristics, and resolve questions that could not be answered when the material was first collected.

Santiago Ron reviewing jars with historical specimens preserved in the collections of the Natural History Museum in London. Specimens were collected in the 19th century in Ecuador and preserved in London. Credit: Santiago R. Ron

In this case, combining 19th-century museum specimens with observations of living populations allowed researchers to formally recognize Pristimantis milpe as a separate species.

The finding also shows that biological surprises are not limited to rare or obscure animals. Even an abundant and familiar frog can remain misidentified for decades, and correcting such errors often requires linking historical collections with modern observations and research tools.

Reference: “Long overdue: a new, widespread, species of Pristimantis (Anura, Strabomantidae) from the Chocó region and the synonymy of Pristimantis subsigillatus” by Santiago R. Ron, Poulette Paredes-Aguirre, Diego A. Paucar, Yaara López, Katherine Apunte and Jhael A. Ortega, 24 July 2026, ZooKeys.
DOI: 10.3897/zookeys.1286.194383

Field and laboratory work in Ecuador were funded by Secretaría Nacional de Educación Superior, Ciencia, Tecnología e Innovación del Ecuador SENESCYT (Arca de Noé initiative; SRR and Omar Torres principal investigators) and a grant from Pontificia Universidad Católica del Ecuador, Dirección General Académica.

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