Disclaimer:

The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

---

Common name: Axolotl

Synonyms and Other Names: Salamandra ajolote, Mexican axolotl

Taxonomy: available through www.itis.gov

Identification: Ambystoma mexicanum are paedomorphic salamanders meaning that they do not metamorphosize into a terrestrial adult form like many other salamander species (Humphrey, 1975). They have external gills that branch from their head giving a crown-like appearance. Along the body of adult A. mexicanum are lateral lines known as costal grooves. Ambystoma mexicanum have a dorsal crest that runs from the tail to the base of the head. This dorsal crest becomes more pronounced as they reach sexual maturity (Clare, 2019).

Size: Adults can reach up to 30 cm in length (Clare, 2019).

Native Range: Ambystoma mexicanum are endemic to the Lake Xochimilco area in the Valley of Mexico (Shaffer, 1989).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Ambystoma mexicanum live in slow-moving water in the wetlands of Lake Xochimilco (Ramos et al., 2025). They thrive in colder waters between 16-20 degrees Celsius (Shaffer, 1989). Abystoma mexicanum are obligate ambush predators that feed on a variety of invertebrates (Zambrano et al. 2010). While they retain their aquatic lifestyle into adulthood, adult A. mexicanum develop rudimentary lungs and can occasionally be seen going to the surface to gulp air (Clare, 2019).  This species does not engage in physical copulation, instead the male leaves spermatophores in the environment which they then convince females to pick up with their cloaca to fertilize during a courtship display (Maex et al. 2016).

Means of Introduction: Ambystoma mexicanum are popular in the pet trade and was most likely introduced from an aquarium release.

Status: The individual found was removed from Walnut Creek (Bartos, 2025). There is no evidence of an existing population of non-native A. mexicanum.

Impact of Introduction: The impacts of this species are currently unknown. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.

Remarks: Ambystoma mexicanum are listed as critically endangered in their native range by the IUCN with primary threats being habitat loss and pollution (Zanbrano et al. 2010). 

Ambystoma mexicanum have a long history of being model organisms in scientific research, specifically their regenerative abilities including being able to regenerate lost limbs (Voss et al. 2009).

References: (click for full references)

Bartos, M. 2025. Axolotl, rare salamander native to Mexico, discovered in Pennsylvania waterway. CBS News. Pittsburgh, Pennsylvania. https://www.cbsnews.com/pittsburgh/news/axolotl-pennsylvania-walnut-creek/. Created on 11/20/2025. Accessed on 11/20/2025.

Clare, J.P. 2019. Biology of Axolotls. https://www.axolotl.org/biology.htm.

Humphrey, R.R. 1975. The Axolotl, Ambystoma mexicanum. In: King, R.C. (eds) Handbook of Genetics. Springer, Boston, MA. https://doi.org/10.1007/978-1-4613-4470-4_1.

Maex, M., I. Van Bocxlaer, A. Mortier, P. Proost, and F. Bossuyt. 2016. Courtship Pheromone Use in a Model Urodele, the Mexican Axolotl (Ambystoma mexicanum). Scientific Reports 6: 20184. https://doi.org/10.1038/srep20184.

Ramos, A.G., H. Mena, D. Schneider, and L. Zambrano. 2025. Movement ecology of captive-bred axolotls in restored and artificial wetlands: Conservation insights for amphibian reintroductions and translocations. PLoS ONE 20(4): e0314257. https://doi.org/10.1371/journal.pone.0314257.

Shaffer, H.B. 1989. Natural history, ecology, and evolution of the Mexican “Axolotls”. Axolotl Newsletter 18: 5-11.

Voss, S.R., H.H. Epperlein, and E.M. Tanaka. 2009. Ambystoma mexicanum, the Axolotl: A Versatile Amphibian Model for Regeneration, Development, and Evolution Studies. Cold Spring Harbor Protocol. https://doi.org/10.1101/pdb.emo128

Zambrano, L., E. Valiente, and M.J. Vander Zanden. 2010. Food web overlap among native axolotl (Ambystoma mexicanum) and two exotic fishes: carp (Cyprinus carpio) and tilapia (Oreochromis niloticus) in Xochimilco, Mexico City. Biological Invasions 12: 3061-3069. https://doi.org/10.1007/s10530-010-9697-8

Zambrano, L., P.M. Reidl, J. McKay, R. Griffiths, B. Shaffer, O. Flores-Villela, G. Parra-Olea, and D. Wake. 2010. Ambystoma mexicanum. The IUCN Red List of Threatened Species 2010: e.T1095A3229615. https://dx.doi.org/10.2305/IUCN.UK.2010-2.RLTS.T1095A3229615.en.

Author: Stratton, L.D.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.