On the scruffy shrublands of the Iberian Peninsula, where the summers are parched and sweltering, it doesn’t take much for a spark to catch. The wildfires burn hot and fast, stripping the soil of its characteristic brush like a close shave. What’s left behind is withered and black, and the air stays stifling for weeks.
It’s all a bit bleak, but the Algerian sand racer, a burrowing, long-tailed lizard, has struck a tentative truce with the flames. It has learned the scent of smoke, and will hide while the conflagration runs its course. When the fires are extinguished, the reptile reemerges into a world that’s not just scorched but, thanks to the burn, a bit more sanitary to live in.
Wildfires kill. Among their casualties are plants and the tiny arthropod parasites that live on and around them. This is terrible news for mites, and excellent news for the lizards they terrorize. Lola Álvarez Ruiz, a biologist at the Desertification Research Center in Spain, compares the pesticide-like flames to a “cleaning effect.” After spending years scampering after hundreds of the region’s lizards and counting their mites, she and her colleagues have uncovered a new connection between wildfires and reptilian public health—one they’re scrambling to understand before climate change further disrupts the peninsula’s natural burns. Even fire-friendly lizards might be doomed to suffer in an overburnt world.
Fires, researchers have long known, can sculpt the environment, not just through direct destruction, but by unraveling the threads that hold an ecosystem together. When they burn certain species away, flames make room for others to flourish in the space they leave behind. They can open up opportunities for hardy pollinators to alight on newly grown wildflowers, and for predators to snare newly exposed prey. Bouts of burning can even influence the transmission of infectious disease, shaping how populations of devastating fungi and infection-toting arthropods wax and wane over time.
Álvarez Ruiz’s recent work adds sand racers to the list of burn beneficiaries. The lizards are highly territorial, and will spend their entire life roaming a swath of land smaller than a backyard swimming pool. Their homebody tendencies make them easy prey for mites, which can pass between lizards when they mate or wrestle for real estate, or jump onto them straight from the soil. The parasites will wriggle beneath the scales on their hosts’ bellies and tails, where they can access blood and other “juicier parts of the lizard,” potentially ferrying in malaria-causing microbes, Christian Cox, a reptile expert at Florida International University, told me. Eventually, the bothersome arachnids detach to complete the rest of their life cycle elsewhere, but the lizards are left marked: Their scales will stay raised like popped collars, souvenirs of the mites’ brief tenure beneath them.
But in fiery places, mites have a weak spot: They must detach from their lizard hosts and seek mates in the soil or within the detritus of dead plants, so any flames that sweep through should, in theory, burn a bunch of these lovelorn pests to a crisp.
To show that fires make a dent in the lizards’ parasitic plight, Álvarez Ruiz and her colleagues trekked into the fire-prone wilds of eastern Spain. They fitted little lassos to the ends of long poles, and spent many sweaty weeks trying to gently loop the nooses around lizards’ heads. The reptiles were wily, and the work was often grueling, especially in areas where the flames had swept through just a few weeks or months before. The team collected animals from badly scorched spots, as well as adjacent plots that had been spared by the flames, and examined them with magnifying glasses to count up their mites. The effects, they found, were most pronounced in places that had burned within the year prior: Only 18 percent of lizards in those areas carried parasites, compared with 74 percent in spots the flames had left untouched.
The lizards’ relief wasn’t permanent. As the months wore on, vegetation slowly rebounded, buoying the prospects for mites. (Many parasites also presumably survived by hitching a ride on lizards as they absconded into their own hidey-holes.) But even lizards in areas that were two, three, or four years out from their most recent wildfires showed signs of leading less mite-y lives, based on the patterns observed in their scales. The youngest lizards seemed to fare the best; “It was very common to see juveniles have zero parasites,” Álvarez Ruiz told me. That can put these little lizards at a big advantage, she added: They hatch into a world that’s pleasantly scorched, and have a shot at living their formative period infection-free.
The researchers didn’t scour the soil for free-living mites, so it’s hard to confirm that the mites were being directly culled by the flames. Deborah Bower, a conservation biologist at the University of New England in Australia, who wasn’t involved in the study, agrees that this was the most likely explanation. But she notes that the researchers can’t rule out other, more lizard-centric possibilities, such as an uptick in reptilian physical distancing. And what’s happening between these lizards and their mites won’t necessarily hold true for other populations, and certainly not other parasites and hosts. Under different circumstances, fires could crowd animals together, making disease transmission more likely; they could toast the ground to a tolerable temperature and make certain parasites thrive.
Most of the ways in which flames skew relationships between plants and animals remain unexplored, but chasing down those answers is urgent, experts told me, because the interspecies tussles we’re observing now might not hold for much longer. As the planet warms and people continue to encroach into wild spaces, fires—both natural and human-made—are arising at a quickening clip and becoming much more difficult to tame. Eventually, the lizards’ détente with the flames may begin to waver, if it’s not breaking already. Too-frequent fires deprive landscapes of the time and space they need to breathe and recover, potentially depriving the lizards of shelter and prey. Even the roasting of mites could ultimately take an ugly turn in an overburnt world. Parasites amp up their hosts’ immune systems. They also keep populations in check, preventing the animals they infect from overrunning their own ecosystem. “Removing them,” Joseph LaManna, an ecologist at Marquette University who wasn’t involved in the study, told me, means “losing antagonists—a destabilizing thing.”
Flames, like pathogens, depend on spread to survive. They hop from host to host, moving more quickly when kindling is close. They’re crucial for balancing out ecosystems, but devastating when left unchecked. The fires that are goaded on by climate change are a symptom of the crisis, but also now part of the threat to the world’s remaining biodiversity. That’s made researchers’ job all the harder: They are trying to catalog a status quo that is rapidly slipping through their fingers. “We’re losing our baseline,” LaManna said. The hope is that we haven’t lost it already.