Monsters in Trouble

Gila monsters are shrouded in mystery. The venomous, desert-dwelling lizards spend most of their lives underground and out of sight, only coming up to the surface occasionally to hunt for food, bask in the sun or find a mate.

These hefty reptiles that look like they’re covered with Halloween-colored beadwork are so introverted that scientists aren’t even certain how many of them exist across their range, which spans the American Southwest and northwestern Mexico. What is known is that their population is decreasing—the International Union for Conservation of Nature lists them as a “near-threatened” species due to challenges like human development and invasive species. 

But for Dale DeNardo, a professor in the School of Life Sciences at Arizona State University who has been studying Gila monsters in his state for nearly three decades, one threat trumps them all.

“Nothing in my mind is close to what the potential impact of climate change is going to do to these guys,” DeNardo said.

Though there is scant research on how Gila monsters might fare in a warming world, a March study published in Ecology and Evolution suggests that their range in the Mojave Desert—considered their northernmost habitat—could shrink significantly under higher emissions scenarios.

Some of the most pressing climate-related threats to the species include a shifting monsoon season and reduced availability of food, researchers note. It’s unclear how far these lizards will go to adapt to a new climate future, and scientists are divided on where to focus their efforts to help the species survive. 

Water Woes

While rising temperatures might be the first challenge that comes to mind for a desert-dwelling species, DeNardo said that’s not much of an issue for mostly nocturnal Gila monsters, who hide out underground and don’t generally have to deal with daytime heat. 

“To me, the biggest risk to these animals is this anticipated change in the precipitation patterns,” he said.

Gila monsters are dependent on the summer monsoon season for hydration, he explained. Most projections suggest that under current climate models, the Southwestern monsoon season, which brings increased moisture and rainfall to the region, will start later in the summer, according to Climate.gov. 

This delay could cost Gila monsters, DeNardo said. Though they can reabsorb the water content of their urine, utilizing their bladder sort of like an internal canteen, this hydration reservoir can only carry monsters so far.

“The problem is that this canteen gives them about 80 days of buffer against a long drought,” DeNardo said. “So they can go 80 days before they get significantly dehydrated.” 

While that’s doable in current conditions, just a half-month delay of the monsoon season could push Gila monsters into dangerous territory, he said. 

“Even with this canteen they have, they’re not going to be able to tolerate this extended longer hot dry season,” DeNardo said.

Landscape and Prey Are Vital

Gila monsters can survive for months without feeding by storing fat in their tails. Still, they need to eat a few large meals per year, with the feasts usually consisting of rodents, birds, insects, eggs and other reptiles. They paralyze their prey with a potent venom that scientists have used to develop drugs that can treat type 2 diabetes. But some experts are worried that climate change could significantly reduce their ability to find food. 

“Gilas are built to survive,” said Leland Pierce, state herpetologist (a reptile and amphibian specialist) at the New Mexico Department of Game and Fish. “But it’s all going to come down to how does changing climate impact their prey?”

Gila monsters can “wait it out,” sheltering underground through a variety of climatic conditions. However, some of the animals that make up their meals might have a harder time adapting to hotter and drier weather. 

“If changing temperatures, changing weather, climates, suddenly impact quail or impact ground nesting doves and those animals disappear, you know monsters are in trouble,” Pierce said. “If ground squirrels don’t have the seeds and the vegetation that they need because of climate change, monsters are in trouble.”

DeNardo agrees that climate change could affect the Gila monster’s food availability, though he doesn’t know to what extent. 

“I would expect that some of their prey species might be more vulnerable than they are to climate change,” he said.

Pierce also noted that Gila monsters’ ability to ride out extreme weather conditions is integrally tied to the availability of underground shelters. Gila monsters generally live in burrows, some of which they dig themselves and others they move into after other desert animals such as tortoises and rodents excavate them. Other monsters live in rock crevices. These hideouts are vital in helping these lizards maintain safe body temperatures.

The subterranean bunkers, which are relatively humid compared to the desert air outside, can also help the lizards limit water loss, and cooler below-ground temperatures allow Gila monsters to reduce their metabolic rates to conserve energy. The underground dwellings also help them to stay safe from predators such as hawks and coyotes. 

“If Gila monsters lose some of their shelters and they cannot get out of a hot sun, then they’re in trouble,” Pierce said.

Several factors can cause these shelters to disappear or degrade, according to Pierce. Drought, for instance, can lead to a loss of plants that provide support for soils, which can drive erosion, causing the shelters to fall apart or fill in. Fire can similarly impact plants and soil structure. And human activity, such as building development, can also reduce the availability of shelters. Meanwhile, climate change, in conjunction with erosion, could cause these hideouts to become too hot or cold for the animals.

“That’s why I feel managing the landscape, managing their prey base, is so vital to keeping Gila monsters around, regardless of what happens with climate change,” Pierce said. “If we [do those things], we’ve got a fighting chance to conserve Gilas.”

Conservationists should be looking at the whole range of challenges facing Gila monsters throughout the year, DeNardo said. “You only get to die once.”  

“So even if 11 and a half months are great and there’s all the food and resources you can imagine … if there’s something lethal just for a given day, you’re dead,” he warned.

Dispersing to Persist

Gila monsters’ survival chances in a hotter world could come down to their ability to relocate. 

Another study in Ecology and Evolution led by a team of U.S. Geological Survey scientists predicts that between 2070 and 2100, suitable habitat for the species will shift northward to places like northern Arizona, Utah, western Colorado, northern New Mexico, much of California and even parts of Idaho, Oregon and Washington, as these areas begin to become more like the Gila monster’s current desert habitat.

But this future, modeled on habitat suitability based on forecasted rainfall patterns and temperatures, largely depends on Gila monsters’ ability to actually move into these areas. Landscape features such as canyons and mountain ranges, along with human developments, could limit their ability to migrate. The model also fails to take into account any relationships Gila monsters may have with specific habitat characteristics such as rock outcrops, vegetation and soils.

“So it’s a good story if animals are able to disperse and to persist and reproduce in those new places,” said Michelle Jeffries, a USGS biologist based in Boise and a co-author of the study, which modeled the geographic extent of suitable climate for 130 reptile species in western North America under six climate change scenarios.

The recent Mojave Desert-based research may give some insight into how this could play out. Study lead Steven Hromada told The Wildlife Society that in some cases, Gila monsters’ ability to move into areas with more suitable temperatures as the climate warms appears to be limited due to landscape features such as cliffs and roads. While Gila monsters can and do cross roadways, vehicle strikes endanger them, he said. Ultimately, his team predicts that the Gila monster’s range in the Mojave will shrink.

Jeffries said this scenario aligns with her team’s results, which also predict possible habitat shrinkage in southern Arizona, northern Mexico and parts of California, New Mexico and Nevada. Basically, if Gila monsters don’t find a way to disperse, their range will contract in a warming world, she said.

DeNardo said that populations on the peripheries of the lizard’s habitats, like those in the Mojave, are more likely to die out as the climate warms. He thinks conservation efforts should focus on the species’ core range in western and southern Arizona and northern Mexico. 

“That core is going to be kind of the last stand for these animals,” he said. “And you don’t want that core to be too small.”

Not everyone agrees. Pierce, for instance, said that New Mexico’s Gila monsters, considered a healthy population on the periphery, “may have a unique suite” of adaptations and genetic makeup that could be useful to future conservation efforts. 

“The value may be in their uniqueness,” he said. “They may be better adapted to handle changing climates than the ones in the core.” 

And the survival adaptations of the peripheral populations could prove helpful even to the Gila monsters at the heart of the lizard’s range.

”Frankly, they may someday want to mix some of our animals with [other populations] to get a really good genetic diversity,” Pierce said. “So we’re trying to keep the animal across this landscape.”