That’s actually part of the danger, says DeNardo. Rattlers are fairly docile in the wild but easily agitated in captivity. Gila monsters are the opposite. “If you take that same lizard and put it in the sun for a few minutes, it’ll turn, hiss at you, and moonwalk away into a bush.”

DeNardo has long been fascinated by the lizards because they live life on the edge. They get all their food—rodent pups, bird chicks, and eggs—by raiding nests, which are few and far between, and only available between spring and late summer. They make the most of whatever they find, eating up to a third of their weight in one sitting and storing fat in their stumpy, bulbous tails, which they live off the rest of the year. But they have to find their meals first. “An egg doesn’t come rolling past, so they can’t be like a rattlesnake sitting in a shady spot and waiting for a rat to run by,” says DeNardo. “They have to be out searching.” And that means braving the scorching desert.

Partly, they cope by having a naturally low body temperature. DeNardo also discovered that they can use their bladders like a giant canteen. If they binge drink in spring, they can fill their bladders to around 20 percent of their body weight—the equivalent of an average human carrying a 30-pound jug of water inside them. With this reservoir, they can go for almost three months without dehydrating.

On their long foraging walks, the sluggish monsters are vulnerable to coyotes and birds of prey. That is probably why they’re venomous. They certainly don’t need toxins to help them to subdue helpless eggs, chicks, and pups. Instead, they use their venom for defense. No one has ever died from a Gila monster bite because the toxins aren’t great at destroying cells and tissues. They do, however, hurt like a sonofabitch.

“It felt like my finger was caught in the door of a car,” says DeNardo of his one and only bite, “and then like being hit by a hammer every ten seconds. For 45 minutes, I couldn’t concentrate.” That was a hatchling too, and one that lightly nipped him. Adults have a reputation for hanging on with bulldog tenacity, chewing as they bite to release more venom. If that happens, “find a tree, sit in the shade, and suffer,” DeNardo advises. “Don’t drive yourself to a hospital. You won’t die from the bite, but you’ll die from an accident.”

“In many ways, this animal is perfect for the desert,” he adds. “They’ve been in the Sonoran Desert since as long as there’s been a Sonoran.”

Studying the Gila monster isn’t just an exercise in academic curiosity. This stumpy lizard has already improved human health. In the 1990s, endocrinologist John Eng identified a protein in its saliva, known as exendin-4, which was similar to a human hormone that controls our blood-sugar levels. It seemed like a promising way of managing type 2 diabetes, especially since it lasted much longer than its human counterpart, and would only need to be injected daily rather than hourly.