Invasion of the bagworms

Invasion of the bagworms

From Downtown Albuquerque News

Between the occasionally dramatic lack of foliage and the very real possibility of running headlong into one of the critters as it dangles from a tree, it’s hard not to notice the show of force put on this year by bagworms, tiny pests that eat leaves by the dozen and costume themselves in the leftovers.

The invasion is particularly prevalent at Mary Fox Park and Washington Middle School Park, as several DAN readers have noted recently. So what’s going on?

Bagworms are actually caterpillars that turn into moths. During that metamorphosis, they feed on tree leaves, said David Lightfoot, the collection manager for the Museum of Southwestern Biology at UNM.

“The caterpillars crawl around on stems and small branches of trees, then they build a little sack made of silk over themselves,” Lightfoot said. “They attach fragments of plant leaves they’re feeding on to the silk bag.”

Though they do eat leaves as they grow into moths, something that might defoliate entire trees, Lightfoot said bagworms rarely cause permanent damage or kill trees.

City spokeswoman Jessica Campbell agreed with that assessment, saying that greater Downtown trees will likely bounce back next year.

“Trees will typically recover unless the same tree is defoliated year after year, faces other stressors, and is left untreated,” she said.

Campbell said city forestry crews are actively monitoring trees in city parks, especially evergreens, for signs of bagworms. If concerned about the health of those trees, crews will treat trees with a nonchemical insecticide, but only in late spring or early summer. The particular insecticide used contains a microbe found naturally in soil that makes proteins that are toxic to bagworm larvae, Campbell said.

If bagworms have become a problem in trees on your property, Lightfoot has an easy solution: Attach a high-pressure nozzle to a garden hose and knock the bags off the tree.

“Once the larvae are on the ground, it’s pretty hard for them to get back up into the tree,” Lightfoot said. “They usually end up feeding on something else, or they die.”

Bagworms will attach just about anywhere on just about any type of tree, but they prefer to feed on younger leaves. When inspecting your trees, Lightfoot said to pay special attention to the outer tips of branches, where the youngest leaves are.

How the bagworm caterpillars get on the tree branches is either interesting or gross, depending on your point of view.

Once the caterpillars pupate and emerge as moths, mating season begins. Female bagworms are flightless and stay put at the site of the bags, emitting pheromones to attract males, who can fly. The female produces eggs and lays them in the bag, or sometimes they stay in her body.

Because female bagworm moths cannot fly, they end up getting eaten by birds, but the eggs survive the digestion process and are deposited by the bird at a new location – sometimes a fresh tree. Caterpillars hatch from those eggs, build bags, feed on leaves, and the process repeats. (Some bagworms also sail around on long strands of silk, a phenomenon known as ballooning.)

Campbell said the city’s 311 service has seen an increase of calls about bagworms this year, indicating they are more prevalent this summer than in years past. However, she said the calls are from all over the city, not just greater Downtown.

“Heading into next spring, we are planning to have educational signs posted in parks we are monitoring so the public knows they are on our radar and can learn a bit more about bagworms,” Campbell said. “Another initiative we are considering is gathering volunteers to remove bagworms from trees. This will not totally eliminate the population, but would help control it.”