What it means
The Gila monster is the desert’s best-dressed reptile: a thick, slow lizard up to 22 inches long, covered in bead-like scales of black and coral-orange, with a fat tail where it stores fat for lean months. It is one of the very few venomous lizards on earth, the largest lizard native to the United States, and a creature most Scottsdale residents have never seen in the wild, because it spends about 90 percent of its life underground.
Locals say the name like they are talking about a celebrity sighting. “We saw a Gila on the trail” gets a crowd around a phone at any dinner party. The desert wildlife field guide describes it as venomous, spectacular and about as fast as a bored housecat, and notes that the bites that do happen almost always happen to someone who picked one up.
Where you’ll meet it
On spring mornings, on rocky slopes and washes in the Preserve and the trails in the north Scottsdale hiking guide; and occasionally on a patio or in a garage at the desert edge, which is when the dogs guide advice to keep a leash on matters.
Where the word came from
Gila is the river: the Gila River basin of Arizona and New Mexico, where the lizard was once plentiful. The river’s name came into English through Spanish, which is why the G is an H and the word is HEE-luh, the same as in Gila Bend and the Gila River Indian Community. “Monster” was the settlers’ contribution, a reputation the animal never earned. The genus name, Heloderma, means “studded skin,” for the beads.
The reputation once nearly finished it. By mid-century, commercial collecting for roadside menageries and zoological supply companies was thinning the population, and plenty of people killed one on sight. In 1952 Arizona made it the first venomous animal in North America to receive legal protection, and other states followed over the next three decades.
The modern word has a second meaning in medicine. In 1992 Dr. John Eng, an endocrinologist at the Veterans Administration medical center in the Bronx, published his isolation of exendin-4 from Gila monster venom. It acts like GLP-1, a human gut hormone that helps control blood sugar, but lasts far longer in the body. A synthetic version, exenatide, was approved by the FDA in 2005 as Byetta, the first drug of the class that now includes the best-known weight-loss medicines.
What it is not
Not a Mexican beaded lizard, its larger, darker cousin to the south. Not a chuckwalla, the big harmless rock lizard of the same slopes. And not aggressive: given room, it walks away.
The fine print
The venom system is unusual. Rattlesnakes inject through hollow fangs; the Gila monster produces venom in glands in the lower jaw, and it flows along grooves in the teeth by capillary action while the lizard chews. That is why a bite is so bad: the animal clamps on and grinds, and the longer it holds, the more venom enters. The Park Service calls a bite a serious medical emergency. Deaths are vanishingly rare, and healthy adults survive, but the pain and swelling are severe.
The lizard’s lifestyle explains why you so rarely see one. It surfaces mornings and evenings in spring and fall, at night in summer, and occasionally to bask in winter, and spends the rest of the time in burrows and rock shelters. It raids nests: baby rabbits and packrats, eggs, nestling birds, small lizards. It can eat up to 35 percent of its body weight at once, and three or four big meals in spring can carry it through the year.
Protection is complete. State law makes it illegal to kill, collect, possess, relocate or harass a Gila monster, and inside national parks federal law applies too. The McDowell Sonoran Conservancy’s 2011 to 2013 reptile survey documented the banded Gila monster in the Preserve, noting it as a species of concern to the U.S. Fish and Wildlife Service. If one turns up in your yard and cannot stay, the answer is a licensed removal service, not a shovel.