Friday Fauna Feature: Gila Monster 

Written by Aleidys Lopez Romero

While our species this week is certainly not the poster-child of “cute and cuddly,” their unique coloration and venomous bites are definitely a showstopper. We were especially excited to see this beautiful and iconic lizard of the region show up finally on our Border Wildlife Study camera array in August 2021 and it remains the only detection we’ve had in the study so far, although we have also had 8 detections on the Sky Island FotoFauna network cameras. This means out of 4 million photos taken with wildlife cameras across the region over the last two years, fewer than 10 Gila monsters were recorded on camera. These orange and black lizards are not common, so consider yourself very lucky if you see one! 

A close-up of two rulers in the dirt measuring the size of two gila monster footprints. They are each roughly 1.5 inches wide (4cm), 2 inches long (6cm), and are 1.5 inches (4cm) apart

Since Gila monsters spend so much time below ground, actually seeing one is unlikely. That said, if you’re in their habitat in the right season, when they’re active – you might see their distinctive tracks in sandy or dusty areas!

Description

Gila monsters (Heloderma suspectum) are one of the few venomous lizards in the world. They grow to be about 20in (50cm) and have chunky tails where they store fat for the winter months. They have warty scales and blotches or stripes of black and pink. Being the largest lizard native to the United States, it is not surprising that Gila monsters need lots of food and rest. In fact, young Gila monsters can eat up to 50% of their body weight in one feeding (Arizona-Sonora Desert Museum: Gila Monster)! Additionally, Gila monsters hibernate from late November to February. In the summertime, female Gila monsters lay eggs ins the summer and leave them! The eggs hatch after ~5 months and the hatchlings remain underground with their egg yolk until late spring/early summer

Diet 

Gila monsters are mostly nocturnal hunters that prey on small mammals, eggs, and birds. Their large size and stocky figure makes them sluggish hunters that focus on technique rather than speed. Their venom oozes out of grooves in their teeth and is injected into their prey with every bite. 

Habitat

Gila monsters spend a large portion of their lives in burrows and tend to linger around 1-2 different burrows in a year, one during hibernation and the other during the summertime. They prefer areas dominated by Saguaro Cacti and Palo Verde trees. Their range spans from the Southwestern United States to Sonora, Mexico. 

A gila monster walked through a dried wash. It is small enough to easily be confused for a rock. Behind it are many green plants.

The first Gila monster of our Border Wildlife Study was documented during the day in August 2021 walking up a sandy wash in the Patagonia Mountains. Can you spot it?

Conservation Status: Near Threatened

Gila monsters’ biggest threats are illegal exploitation by collectors and habitat destruction due to urbanization and agricultural development (IUCN Red List). Fortunately, law enforcement has helped these lizards by making it illegal to collect, sell, or kill them in Arizona. 

Fun Fact

Gila Monsters gained legal protection in Arizona in 1952 making them the first venomous animal in North America to be protected by law (Arizona-Sonora Desert Museum: Gila Monster)! 

Learn more about other species we commonly see in our Border Wildlife Study here. 

Sources

National Geographic

Arizona-Sonora Desert Museum: Gila Monster

Britannica

IUCN Red List