Killing a tamarisk tree is a tough job.
Unless you’re a hungry tamarisk beetle. Then it’s just lunch.
In their native Asia, the trees and beetles live in equilibrium. But when tamarisks were introduced to the West in the 1800s for ornamentation and erosion control, the plants had no natural enemies to keep them in check. They soon ran wild across the Colorado River Basin and began to wreak havoc on native ecosystems.
Two decades ago, Utah officials responded by releasing thousands of the beetles near Moab. Their assignment was simple: Enjoy the tamarisk buffet.
Like humans enlisting Godzilla to battle other monsters we’d have little hope of defeating, the idea was to let them fight. And for years, it was scientist Tim Graham’s job to see who was winning.
“Every year, I would do eight surveys,” he said. “Come out, stare at the foliage and look for beetles. Count how many I could see in 15 seconds.”
Graham rummaged through the bare limbs of a mostly dead tamarisk tree just outside Canyonlands National Park to demonstrate the process. His tightly braided grey ponytail dangled as he ducked below a branch and looked upward, inspecting it for beetle activity.
He did this kind of thing a lot between 2014 and 2023 when he led programs monitoring the bugs’ progress in this part of southeast Utah’s red rock country. A retired insect ecologist, Graham moved to Moab in 1984 and worked for decades with the National Park Service and other agencies on invertebrate research.
Unlike other beetles that kill pine forests in the West, tamarisk beetles don’t have a taste for native plants. The U.S. Department of Agriculture recommended them as a biological control for tamarisk trees (also known as saltcedars) beginning in 2003, after conducting studies that showed the bugs posed little threat to the ecosystem.
The following year, the six-legged eating machines were released in Grand County. And Graham has been happy to do his part.
“We don't have enough Lorax-type people speaking for the trees and the bees and the shrubs and the rocks and everything to offset some of the folks that speak with their wallets,” he said. “That's the thing that concerns me a lot. This is the only Earth we've got.”
Wearing a short-sleeved shirt dotted with red, blue and yellow bugs, Graham pulled out an old iPhone box where he’s stashed a few of his former coworkers. The tamarisk beetles inside are about the size of a ladybug, but thinner, with a drab greenish-yellow and brown pattern on their back that resembles a shield.
The bugs may be tiny, but when they swarm to feed, they pack a punch. They repeatedly consume the tamarisks’ leaves and bark until the green trees gradually turn brown and die.
While the insects may have done most of the hard work, Graham’s job was no cakewalk. He crisscrossed hundreds of miles of Grand County to regularly survey around 60 test subject trees, including the one near Canyonlands. He cataloged the beetles’ impacts and often had to crawl through thickets to collect his data.
When he sees dead tamarisk trees around Moab today, though, all the beetle project work feels worth it.
“That's shade that isn't covering the ground and keeping other things from growing. It's resources that other plants can have,” he said. “All in all, it's about as good a success as we could expect.”
Graham doesn’t let the dead tamarisk go to waste, either. He carves letter openers, hairpins and earrings from the wood in his spare time.
Even though he doesn’t gather official data anymore, he still enjoys examining a branch or two. After so many years of getting to know these particular trees, it would be hard to stop.
“I'll keep an eye on them,” he said. “And if we stop getting brown tamarisk, then I'll start to get worried.”
A mature tamarisk can live up to 100 years and produce 600,000 seeds annually. The trees now smother a million acres of the Southwest, ravaging riverbanks from Texas to California.
Once established, the tamarisk steals water from the shrinking Colorado River and pushes out native plants, such as the cottonwood. It grows densely, cutting off sunlight to nearby vegetation and converting previously diverse landscapes to tamarisk monocultures. And as its leaves fall to the ground, they make the soil too salty for other plants and increase wildfire risk.
On top of that, they are hard to kill. They regrow quickly after being burnt or cut, and often require intensive herbicide treatments.
“Over the years, we've learned that they're more harmful than we thought they were,” Graham said. “So when the beetles started working out, then it was really welcomed by most people.”
The beetles haven’t been embraced universally, though.
After studies warned their handiwork may harm the endangered southwestern willow flycatcher, a bird that had begun nesting in tamarisk trees, the USDA ended its beetle release program in 2010. Arizona has since tried to stop the beetles from spreading there for the same reason.
By that time, however, states across the Colorado River Basin, including Utah, California, Colorado and Wyoming, had already introduced them. Self-sustaining beetle populations have since grown and spread throughout the Southwest.
“The beetles are in control of their own destiny, I think, at this point,” Graham said
Research informed by his monitoring shows the beetles’ voracious appetites have begun to make a dent in tamarisk numbers in Grand County.
At the edge of the Colorado River northeast of Moab, Graham pointed down the bank toward the dark blue water. Bunches of feathery green tamarisk leaves clouded the view.
It’s not realistic to think the beetles could ever eat the trees to extinction, he said. The hope is they can weaken tamarisks just enough so native plants have a chance to make a comeback.
“We're entering a new phase” that’s different from both the ecosystem’s natural condition and the tamarisk-dominated condition of the 1900s, he said. “We'll see what happens. Another big experiment.”
This story was produced as part of the Colorado River Collaborative. KSL TV photographer Mark Wetzel contributed to this story.
