The showrunner of the Angeles National Forest isn’t a 500-pound black bear or a stealthy mountain lion.

It’s a small ant.

The velvety tree ant forms a millions-strong “social insect carpet that spans the mountains,” said Joseph Parker, a biology professor and director of the Center for Evolutionary Science at Caltech. Its massive colonies influence how fast plants grow and the size of other species’ populations. That much, scientists have known.

Now Parker, whose lab has spent 8 years studying the red-and-black ants, believes they’ve uncovered something that helps answer a key question about evolution.

In a paper published in the journal “Cell,” they break down the remarkable ability of one species of rove beetle to live among the typically combative ants.

The beetle, Sceptobius lativentris, even smaller than the ant, turns off its own pheromones to go stealth. Then the beetle seeks out an ant — climbing on top of it, clasping its antennae in its jaws and scooping up its pheromones with brush-like legs. It smears the ants’ pheromones, or cuticular hydrocarbons, on itself as a sort of mask.

Ants recognize their nest-mates by these chemicals. So when one comes up to a beetle wearing its own chemical suit, so to speak, it accepts it. Ants even feed the beetles mouth-to-mouth, and the beetles munch on their adopted colony’s eggs and larvae.

However, there’s a hitch. The cuticular hydrocarbons have another function: they form a waxy barrier that prevents the beetle from drying out. Once the beetle turns its own pheromones off, it can’t turn them back on. That means if it’s separated from the ants it parasitizes, it’s a goner. It needs them to keep from desiccating.

“So the kind of behavior and cell biology that’s required to integrate the beetle into the nest is the very thing that stops it ever leaving the colony,” Parker said, describing it as a “Catch-22.”

The finding has implications outside the insect kingdom. It provides a basis for “entrenchment,” Parker said. In other words, once an intimate symbiotic relationship forms — in which at least one organism depends on another for survival — it’s locked in. There’s no going back.

Parker, speaking from his office, which is decorated in white decals of rove beetles — which his lab exclusively focuses on — said it pays to explore “obscure branches of the tree of life.”

“Sceptobius has been living in the forest for millions of years, and humans have been inhabiting this part of the world for thousands of years, and it just took a 20-minute car ride into the forest to find this incredible evolutionary story that tells you so much about life on Earth,” he said. “And there must be many, many more stories just in the forest up the road.”

John McCutcheon, a biology professor at Arizona State University, studies the symbiotic relationships between insects and the invisible bacteria that live inside their cells. So to him, the main characters in the recent paper are quite large.

McCutcheon, who was not involved with the study, called it “cool and interesting.”

“It suggests a model, which I think is certainly happening in other systems,” he said. “But I think the power of it is that it involves players, or organisms, you can see,” which makes it less abstract and easier to grasp.

Now, he said, people who study even smaller things can test the proposed model.

Noah Whiteman, a professor of molecular and cell biology at UC Berkeley, hailed the paper for demystifying a symbiotic relationship that has captivated scientists. People knew Sceptobius was able to masquerade as an ant, but they didn’t know how it pulled it off.

“They take this system that’s been kind of a natural history curiosity for a long time, and they push it forward to try to understand how it evolved using the most up-to-date molecular tools,” he said, calling the project “beautiful and elegant.”

As for the broader claim — that highly dependent relationships become dead ends, evolutionarily speaking, “I would say that it’s still an open question.”

Residents and advocates gathered Saturday to demand the ban of a chemical that’s used at a Torrance oil refinery and that they say has the potential to cause a mass casualty disaster.

Hydrofluoric acid is used in about 40 gasoline refineries across the United States, according to the National Resources Defense Council. The defense council states that “exposing as little as 1% of a person’s skin to HF (about the size of one’s hand) can lead to death. When inhaled, HF can fatally damage lungs, disrupt heart rhythms, and cause other serious health effects.”

The Torrance Refinery uses modified hydrofluoric acid, or MHF, which the refinery considers to be a safer alternative to HF, though the claim is disputed by advocates. Steve Goldsmith, president of the Torrance Refinery Action Alliance, which hosted the Saturday event, said that if MHF were to be been released into the air, it would create irreversible health effects within 6.2 miles of the refinery, trickling into other parts of Los Angeles County.

And in 2015, he said, this almost happened.

On Feb. 18, 2015, there was an explosion at the refinery, then operated by ExxonMobil, caused by the rupture of an eroded valve. The incident, which released flammable hydrocarbons, injured four workers and forced 14 schools into lockdown.

The Saturday event, held at North High School’s Performing Arts Center in Torrance, marked the 11th anniversary of the explosion.

Goldsmith described the chemical as “murderous.”

“Torrance Refinery had an enormous explosion, and a piece of equipment the size of a bus came within five feet of the hydrofluoric acid, causing a near miss,” Goldsmith said. “We’ve been working to get rid of it.”

Residents like Christopher Truman say replacing MHF with an alternative option is the least that can be done. His parents live near the refinery.

“I’m born and raised in the South Bay, and my family lives in, effectively, what would be the blast radius if another accident happened,” Truman said. “So just in that aspect, I’m very worried about it.”

MHF is also used to clean semiconductor surfaces and produce pesticides and herbicides in the agricultural and pharmaceutical industries, according to the Torrance Refinery.

County Supervisor Janice Hahn said residents should not assume “they will be lucky” if another refinery accident were to occur.

“Only two refineries in California use MHF, Torrance Refinery and the Valero Refinery in Wilmington,” Hahn said. “MHF is simply too dangerous to use. It is a flesh-eating, low-crawling, toxic vapor cloud. Our communities will not be safe until this chemical is gone.”

Goldsmith said a Chevron refinery in Salt Lake City found an ionic-liquid alkylation process as an alternative to MHF. He added that the 2025 Chevron refinery explosion in El Segundo “would have been different if they had been using MHF.”

“They used another chemical that did not endanger the community,” Goldsmith said. “And that’s the thing about refineries, they have explosions. But that’s why you can’t have [MHF] around things that can blow up.”

U.S. Representative

U.S. Rep. Maxine Waters (D-Los Angeles) appears on a video message explaining her legislation, which she says will have a positive impact for communities in the Los Angeles region.

(Allen J. Schaben / Los Angeles Times)

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U.S. Rep. Maxine Waters, (D-Los Angeles), who represents the city of Torrance, greeted attendees in a prerecorded message, in which she reintroduced her bill, the “Preventing Mass Casualties from Release of Hydrofluoric Acid at Refineries Act,” which targets plants using MHF.

“I originally introduced this bill in December of 2024,” Waters said in the video. “I faced considerable opposition, especially from the United Steel Workers Union, [who were] concerned that if refineries converted to safer technologies, some of the refineries might close, leaving workers without jobs. They agreed with me that hydrofluoric acid is dangerous. But they still would not support my bill. So I decided to go ahead and reintroduce this bill, [without] union support.”

The bill would give refineries five years to find an alternative to the dangerous chemical. Violators may be subject to fines up to $37,000 per infraction.

Los Angeles County Supervisor Janice Hahn speaks out against the use of hydrofluoric acid.

(Allen J. Schaben / Los Angeles Times)

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Some residents stressed the need for transparency from local officials.

Ian Patton, a Long Beach resident, said most parts of the investigation into the 2015 explosion were withheld.

“Why can’t they not make this report public? The [Torrance Refinery Action Alliance] has been asking for it for years,” Patton said. “The next step was to look at litigation under the California Public Records Act. It’s not something that we want to do, but the public deserves to know whether these plants are safe.”