The boxwood moth (also called the box tree moth) is an invasive pest whose caterpillars feed aggressively on boxwood plants, capable of completely stripping a shrub of its leaves and eventually killing it. Native to East Asia, it has spread across Europe and now into parts of North America, where it threatens one of the most widely planted landscape shrubs on the continent.
What the Boxwood Moth Looks Like
Adult boxwood moths are medium-sized with white wings bordered by a dark brown band. They’re mostly active at night and are attracted to light, which is often how homeowners first notice them. The adults themselves don’t damage plants. It’s the larval stage that causes destruction.
The caterpillars are the real concern. They’re green with dark stripes running along their bodies and can grow up to 1.5 inches long. Young caterpillars are small and hide among the inner twigs and leaves of boxwood shrubs, making early detection difficult. When they’re ready to pupate, they wrap themselves in webbing tucked inside the plant’s foliage.
Signs of Infestation
Boxwood moth damage often goes unnoticed until it’s advanced, partly because the caterpillars feed from the inside of the shrub outward. Here’s what to look for:
- Skeletonized or missing leaves: Caterpillars chew through leaf tissue, leaving behind only the veins, or consume entire sections of foliage.
- Webbing: Fine silk threads woven between leaves and branches, similar to what you’d see with spider mites but thicker and more concentrated.
- Frass: Tiny pellets of sawdust-like excrement scattered on leaves and at the base of the plant.
- Brown, dry leaves: Sections of the shrub that turn brown and papery, especially in the plant’s interior.
In heavy infestations, caterpillars don’t stop at the leaves. Once the foliage is gone, they feed on the bark itself. This is the tipping point: bark stripping cuts off the plant’s ability to transport water and nutrients, and at that stage, the boxwood typically dies. A single generation of caterpillars can defoliate a mature shrub if the population is large enough.
Where It Has Spread
The boxwood moth arrived in North America through the nursery trade, likely hitchhiking on imported boxwood plants. Confirmed detections have triggered federal quarantines in multiple states. As of mid-2025, the USDA has quarantined several counties in Maryland (Allegany, Frederick, Garrett, and Washington Counties) and Franklin County in Pennsylvania following confirmed moth detections.
These quarantines carry real consequences for the nursery industry and homeowners alike. Boxwood plants cannot be moved interstate from quarantined areas unless the establishment operates under a compliance agreement and ships with a state-issued certificate. The USDA prohibits movement of all other boxwood material from quarantined zones, including cuttings, clippings, debris, and any part of the plant, alive or dead, except for decorative purposes. If you live in or near a quarantined area, moving boxwood trimmings or yard waste could inadvertently spread the moth to new regions.
How to Manage Boxwood Moth
Biological Pesticides
The most widely recommended treatment is a naturally occurring soil bacterium sold commercially as a biopesticide. Products containing this bacterium (sold under names like Dipel, Javelin, and Deliver) work by producing proteins that are toxic specifically to caterpillars when they ingest treated foliage. The key advantage is precision: it kills the moth larvae while posing minimal risk to bees, birds, and other non-target organisms.
Timing matters. These products work best when caterpillars are small and actively feeding, so applications should target early larval stages. Because the bacterium breaks down in sunlight, reapplication is often necessary, especially after rain. A related bacterial strain, sold under names like XenTari and Agree, works through the same mechanism and is also labeled for boxwood moth caterpillars.
Physical Removal
For small infestations or individual garden specimens, hands-on methods can help. Inspect the interior of your boxwoods regularly, parting branches to look for caterpillars, webbing, and frass deep inside the canopy where they prefer to hide. Handpicking caterpillars and pruning out heavily infested branches reduces populations without chemicals. Pheromone traps designed for boxwood moths can help you monitor adult activity and time your other control efforts more effectively, though traps alone won’t eliminate an infestation.
Natural Predators
Some native insects have started to take notice of this new food source. Yellowjackets have been observed grinding up boxwood moth caterpillars to feed to their young. Assassin bugs, including the wheel bug, have been found crawling through heavily infested boxwoods. These are encouraging signs, but their overall impact on boxwood moth populations in North America hasn’t been measured yet. The moth evolved in Asia with its own set of natural enemies, and North American predators are still catching up. For now, relying on natural predators alone isn’t a realistic management strategy.
Protecting Your Boxwoods
Regular inspection is the single most important thing you can do. Check your boxwoods every few weeks during the growing season, focusing on the dense interior where caterpillars hide. Early detection makes every control method more effective. A light infestation caught early can be managed with a single round of biological pesticide or even handpicking. A heavy infestation discovered after bark stripping has begun may mean losing the plant entirely.
If you’re buying new boxwood plants, purchase from reputable nurseries and inspect them carefully before planting. Look inside the foliage for webbing, caterpillars, or green pupal cases. This is especially important if you’re in or near a quarantined area, since the moth’s primary mode of long-distance spread is through the movement of infested plant material.
Gardeners in areas where boxwood moth is established are also beginning to consider diversifying their landscapes. Boxwoods have long been a default choice for hedges and formal gardens, but planting alternatives in at least some areas reduces the risk of losing an entire landscape to a single pest. Inkberry holly, Japanese holly, and certain dwarf yews can fill similar visual roles without the vulnerability to this particular moth.