The tree worms have taken over in Dannielle Mastello’s north Fort Worth neighborhood. When wind speed picks up, she can see the tiny green caterpillars all over her garden. One time, Mastello swears, the “nasty little things” landed in her hair.

“They have decimated every single tree in my neighborhood, probably in the hundreds,” Mastello said. “They came through so fast. I didn’t even realize what was going on until I came out one morning, and I just happened to look up and thought: ‘Oh my God, like half of my tree is gone.’”

In the month since record rainfall hit the Dallas-Fort Worth region, arborists have fielded frantic calls about an invasion of Sciota celtidella, a moth species that targets native hackberry trees. Photos posted by residents show green caterpillars eating leaves bare and covering trees in white cocoons. 

At the Texas Trees Conference of arborists in Waco this week, the outbreak was the talk of the town, said Matthew Clemons, a registered arborist in Fort Worth and owner of While the last noticeable wave of worms hit Texas in 2015, this invasion is much more widespread, he added. 

“It just pops up, and before you know it, every tree is impacted,” Clemons said. “I’ve been from Dallas-Fort Worth and as far south as The Woodlands in the last few days. It’s all up and down the center of the state, so it’s not just Dallas-Fort Worth.”

This fall has also produced a “biblical plague” of aphids and other insects secreting sugar-rich honeydew as they feed on pecan tree leaves, Clemons said. There’s no point in treating the leaves with pesticides when they’re about to fall in October, he added, so residents will just have to put up with the sticky situation.

“I have gotten call after call with people saying: ‘What the heck is going on?’” Clemons said. “They’re washing their cars, they’re washing their windows and everything’s a total mess, more so than normal, under pecans this year.”

Fort Worth’s Blue Ox Urban Forestry has also received an increased number of calls over the past two months regarding hackberry tree invasions and other pest issues driven by the heavy rains, said Mike Hartford, the company’s lead arborist. 

The incredibly hot and dry summer means that the life cycles of various insects and pests were crunched down into the later part of the summer following the August rainfall, Hartford said. 

“Normally, we’d have several months of weather where you can reproduce and have successful breeds of different insects,” he said. “This year, it’s all condensed to one short period of time, so we see the effects a lot more amplified.” 

By the time people see the symptoms of this “unique” hackberry invasion, the damage is already done, Hartford said. But residents don’t have to worry that these worms will invade other species of trees because they’re confined to the hackberry, which is typically a fence-line tree and not the centerpiece of a property, he said. 

This worm attack doesn’t typically warrant costly, invasive treatment, Clemons said. Healthy trees will remain defoliated – without leaves – for the rest of the year and endure a premature fall season before growing leaves again next spring, Hartford said. 

Heavily affected trees could enter next year “a little stressed out,” thanks to the worms and the extensive drought of the past summer, Clemons said. 

“It’s going to have less stored energy to pull from, which could mean smaller leaf surface area on the leaves next spring,” he said. “It could mean a delay in refoliation (regrowing leaves) and could also mean a sparse canopy in general.” 

For residents who want to rid their trees of the green pests, old-fashioned spraying of spinosad pesticide or a pyrethroid insecticide does the trick – but only if you catch the outbreak early, when there are only small signs of the caterpillars, Clemons said. Otherwise, the treatment will be largely ineffective. 

Another way to prevent future outbreaks is using a method known as a basal drench. An arborist will apply a pesticide at the tree’s base so that the roots will absorb it and spread the pesticide through the tree’s system. 

“When these things hatch up and they want to start feeding on leaves, they’d find the leaves distasteful and wouldn’t feed off,” Clemons said. “That’s all that can really be done.” 

Hartford advises residents to avoid applying pesticides to hackberry tree worms if they can. 

“I wouldn’t recommend treatment because you’re just adding a lot of chemicals and potentially killing other insects for not really any purpose because, even if you didn’t treat these caterpillars, they’re not going to damage the trees to the point where it’s going to kill them or anything like that,” Hartford said. “Really, it’s just excessive management and excessive use of chemicals.” 

Mastello didn’t want to take any chances after a summer filled with extreme heat and severe drought. She treated her lawn with pesticides to clear her grass of the caterpillars. 

“It was kind of like instant karma. I felt like they deserved it after eating my trees,” she said. “This whole summer is just pretty much done. This is like the final straw.” 

Haley Samsel is the environmental reporter for the Fort Worth Report. Her position is supported by a grant from the Marilyn Brachman Hoffman Foundation. Contact her by email or via Twitter.

At the Fort Worth Report, news decisions are made independently of our board members and financial supporters. Read more about our editorial independence policy here.

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Haley SamselEnvironmental Reporter

Haley Samsel is the environmental reporter for the Fort Worth Report. You can reach them at Her coverage is made possible by a grant from the Marilyn Brachman Hoffman...