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Many homeowners consider moths relatively benign insects. Some are even pretty cute. But while they may not bite, sting, or cause huge problems while hanging around near your porch lights all night, a few can cause serious problems for trees, shrubs, and other plants.
The box moth (Cydalima perspectalis) is a perfect example. An insect that’s causing problems across portions of Michigan (as well as other midwestern states and large swaths of Europe), box moths are certainly not a welcome sight for homeowners in our area.
We’ll explain everything you need to know about these bugs, including the basics of their biology, the plants they threaten, and the treatments that may keep your landscape safe, below.
The Box Moth’s Invasive History
The box moth (which is sometimes called the box tree moth or BTM) is native to a large portion of East Asia, from the Korean Peninsula to eastern India.
In its home range, it is a fairly insignificant insect, which does not serve as a major pest of Asian boxwood species. This is likely due to a combination of natural predators and parasites that keep its population in check, as well as some natural immunity the local boxwoods have evolved over time.
However, it was accidentally introduced to Europe in the early 2000s, with the first documented appearance occurring in 2007. Europe is home to several native boxwood species but lacks any specialized box moth predators. So, the insect spread rapidly, causing widespread destruction as its range expanded.
By 2018, the box moth had made its way to North America. It was first discovered in Toronto, but it rapidly spread to the U.S., and is currently known to exist in Delaware, Massachusetts, New York, Ohio, and — as you may suspect by this point — Michigan.
Basic Box Moth Biology
As is the case for many other destructive moth species, it is the larval life stage (caterpillar) of the box moth that causes the most damage. In fact, adult box moths have non-functional mouthparts; they don’t eat at all. But the caterpillars have powerful, leaf-crunching jaws that make quick work of boxwood foliage.
Box moth caterpillars begin appearing with the arrival of warm spring temperatures, as many hatch the previous year and overwinter in sheltered spots throughout the landscape. The caterpillars are lime green in color with dark heads and short hairs. As they pass through several developmental stages called instars, they begin developing stripes.
Upon reaching their fifth instar, the caterpillars feed for a little while longer before spinning silken cocoons. They metamorphose in these cocoons over several weeks before emerging as moths. The moths come in two color varieties — light and dark. However, it appears that the light color variety is most common in North America.
Shortly after emerging from their cocoons, the moths will mate, deposit eggs, and begin the cycle anew.
Hosts: Species Vulnerable to Box Moth
Box moths primarily feed on boxwood trees and shrubs (genus Buxus). Because East Asia is the epicenter of Buxus diversity, the moths feed on dozens of different species in their homeland. They also feed on native boxwood species in Europe.
However, there are no boxwoods native to the U.S. Most of the boxwoods found within our borders are members of one of the following species:
- Common boxwood (Buxus sempervirens)
- Japanese boxwood (Buxus microphylla)
- Chinese boxwood (Buxus sinica)
- Cultivars created from hybrids of these species
Nevertheless, box moths feed on all of these species; none are immune to the insect’s feeding activity. Additionally, box moths have been documented feeding on a few other species in some cases. These include:
- Spindle trees (Euonymus spp.)
- Hollies (Ilex spp.)
- Orange Jessamine (Murraya paniculata)
Box Moth Treatment
There are a number of strategies that can be used to address box moth infestations. Some of the most important and useful are described below:
- Monitoring: While not a true “treatment,” it’s important to inspect your boxwood shrubs regularly to give you the best chance of detecting them early, when any treatment will be most effective. Be sure to look for the defoliation they cause, the caterpillars, and the silken webbing they often create.
- Btk: An abbreviation for Bacillus thuringiensis kurstaki, this is a naturally occurring soil bacterium that works as a biological control mechanism for box moth. Commercial preparations are available, which can be sprayed on your boxwoods about three times per year to stop the insects from feeding on your plants.
- Chemical Insecticides: Several products, including spinosad, bifenthrin, and carbaryl, can be used to kill box moth caterpillars. While effective, these insecticides can harm beneficial insects and even lead to growing populations of secondary plant pests, such as some boxwood-feeding mites.
- Hand Removal: Though laborious, you can keep box moth caterpillar populations low (or even eliminate them entirely in some cases) by simply plucking them from the plants and dropping them in a bucket of soapy water. This will obviously be most effective when infestations are caught early.
Special Note: If you find it necessary to remove boxwoods after a box moth infestation, be sure that you double-bag the plant material before disposal to help prevent the further spread of the pest.
Box Moth Quarantine Zone
Given the significant threat the box moth presents (nearly 75% of boxwoods in Europe have died at the hands of this pest), the Michigan Department of Agriculture and Rural Development has instituted a quarantine zone in 2023 to help prevent the insect’s spread.
Special restrictions have been put into place regarding the movement of boxwood plants within this zone, and nurseries must complete compliance agreements, testing programs, and training if they plan on moving boxwoods out of this quarantine zone.
Currently, the quarantine zone includes 13 counties in Southeast Michigan, including:
- Clinton
- Eaton
- Ingham
- Lapeer
- Livingston
- Oakland
- Jackson
- Washtenaw
- Wayne
- Lenawee
- Monroe
- Macomb
- St. Clair
Officials have published an online portal for residents who live outside of this quarantine zone to report sightings of the caterpillar or moth.
Longtree Tree Service: Comprehensive Box Moth Treatments
Whether you are already seeing box moth caterpillars defoliating your hedges or you’re considering replacing your boxwoods with another species, the Longtree Tree Service team can help. We not only have expertise with this invasive pest but also the other common plant and tree diseases in Southeast Michigan.
Contact us today to schedule a free on-site evaluation and estimate.
Sources & References
- Ohio State University Extension – “Box Tree Moth”
This fact sheet provides an overview of the identification, life cycle, and potential impact of the box tree moth on residential and commercial landscapes in Ohio.
https://ohioline.osu.edu/factsheet/ent-0099 - Ohio State University Extension – “Management of Box Tree Moth in the United States”
This technical guide outlines the latest integrated pest management strategies and chemical control recommendations for mitigating box tree moth infestations.
https://ohioline.osu.edu/sites/ohioline/files/imce/Entomology/ENT-0101-Box-Tree-2025-0624-TV.pdf - Michigan State University Extension – “Insecticide Options for Box Tree Moth Management”
This research-based resource evaluates the efficacy of various insecticides for controlling box tree moth larvae while minimizing environmental impact.
https://www.canr.msu.edu/resources/insecticide-options-for-box-tree-moth-management-ir4-project - Michigan State University Extension – “Safeguard Against Spreading the Invasive Box Tree Moth”
This publication provides actionable advice for homeowners and professionals on how to prevent the accidental transport and spread of this invasive pest.
https://www.canr.msu.edu/news/safeguard-against-spreading-the-invasive-box-tree-moth - Michigan State University Extension – “MDARD Establishes Box Tree Moth Quarantine in Four Southeast Michigan Counties”
This news release details the official quarantine boundaries and regulatory requirements implemented to contain the box tree moth within specific Michigan regions.
https://www.canr.msu.edu/news/mdard-establishes-box-tree-moth-quarantine-in-four-southeast-michigan-counties - U.S. Department of Agriculture Animal and Plant Health Inspection Service – “Box Tree Moth”
This official federal resource provides national-level data on the distribution, detection, and management of the box tree moth across the United States.
https://www.aphis.usda.gov/plant-pests-diseases/box-tree-moth
