Gila Monster - KS

The Gila monster is a large bodied venomous lizard around 50cm in length, which mainly lives in the Sonoran Desert of Arizona and Mexico and can live for around 20 years. Gila monsters are mostly active from early March to mid-November, and may be seen basking at the entrances to their shelters in winter and early spring. During hibernation, it is estimated that they spend up to 98 percent of their time in their subterranean shelters. They can vary the time of day that they are active to reduce exposure to temperature extremes – for example, they are active during the day/twilight during the cool wet season and become nocturnal during the hottest seasons of the year.

Gila monsters are often found in the bajada (flat surrounding hills, avoiding open areas) in their active season to rocky hillsides and foothills and grasslands in the winter. Gila monsters stay in burrows dug with their snout or claws, or even occupy empty burrows that other animals have made.

Gila monsters have a relatively high evaporative water loss rate for their size compared to other lizards, and they use this evaporative cooling to reduce body temperature if it gets over 37.5°C. They can also maintain favourable body temperatures by foraging infrequently and selecting thermally favourable places to hibernate. They have a fat tail which stores fat to provide energy during hibernation. It also leaves the rest of the body relatively cool.

Similarly to many amphibians, gila monsters use their urinary bladder as a water reservoir. They stre water in their bladder and absorb it over several weeks to prevent dehydration. A full bladder can contribute an additional 15-20% of total body water to the lizard. This not only prevents dehydration during hibernation or hot summer months, but also allows them to have a high evaporative water loss rate so that the can cool down.