Gila Monster Classification

Gila monster in cage
This is the first scientific illustration of a Gila monster. This female specimen was collected in 1855 on the boundary survey after the Mexican-American war.

One of the most important events in the history of the American Southwest was the establishment of the United States-Mexico boundary between 1849 to 1857. As a result of the Mexican-American War (1846-48) and the resultant Treaty of Guadalupe Hidalgo, the 2,000 mile border between the US and Mexico was established. The results of this survey were reported in the three-volume work, Report on the United States and Mexican boundary survey, made under the direction of the secretary of the Interior by William H. Emory, (1857-1859). In addition to establishing this new boundary, the report is also remarkable in its contribution to understanding of the natural history of the area.

In the summer of 1855, camped southwest of Tucson, a survey team was about to get some relief from the oppressive heat.

Whilst encamped here, heavy storms of wind, hail, and rain, were experienced; the valley where the party lay was so quickly flooded as to endanger all the camp equipage, as well as instruments; tents were blown down, and many articles were carried away by the hurricane. Notwithstanding the inconvenience attending them, the rains were welcome, as they refreshed and cooled the atmosphere, which oftentimes heated to 110° Fahrenheit.

Report of the United States and Mexican Boundary Survey, 1857

These monsoon rains also brought a female Gila monster (drawn in the above lithograph) above ground where it was collected by civilian surveyor Arthur Schott.

Some strange specimens of natural history were found at this place; amoung them, what is called by the Mexicans "El Scorpion," a large, slothful lizard, in the shape of a miniature alligator, marked with red, black and white belts--a hideous-looking animal.

Report of the United States and Mexican Boundary Survey, 1857

Not recognized at the time as a distinct species, this specimen was misidentified as the previously described Mexican beaded lizard, Heloderma horridum (Wiegmann, 1829).  It would be more than 10 years later that Edward Dinker Cope, in 1869, described these animals as a distinct species and called them Heloderma suspectum. Cope gave them the specific name "suspectum" because, at the time, they were suspected to be venomous. Controversy over the question of their venomous nature would continue into the 20th century.

Scientific Classification

  • Kingdom: Anamalia
  • Phylum: Chordata
  • Class: Reptilia
  • Order: Squamata
  • Family:Helodermatidae
  • Genus: Heloderma
  • Species: H. suspectum

Binomial Name

Heloderma suspectum (Cope, 1869)

Recognized Subspecies

H. s. suspectum, Reticulate Gila monster
H. s. cintum, Banded Gila monster