Christelle Guédot, Bryan Jensen, and PJ Liesch, UW-Madison Entomology
Revised: 1/23/2026
Item number: XHT1236
Brown marmorated stink bug (BMSB), Halymorpha halys, is an exotic, invasive insect native to parts of east Asia. BMSB was first confirmed in the United States in 2001, but likely arrived in the 1990’s. BMSB adults are good hitchhikers, which contributes to their spread. By 2025, BMSB has been found in most states in the contiguous United States. BMSB was first detected in Wisconsin around 2010 and has since increased its presence. It has been detected in 50+ Wisconsin counties and has the strongest presence in south-central, southeastern, and east-central Wisconsin.
Appearance
BMSB adults are very similar in size, shape and appearance to native stink bugs in the genus Euschistus. They are approximately ½ to 5/8 inch long, have the typical “shield”-shaped bodies of other stink bugs, and are mottled brown to gray in color. The most identifiable characteristics of BMSB adults are the alternating light (whitish) and dark brown spots on the abdomen where it protrudes beyond the edge of the wings (see photo above). Their antennae are brownish with two pale bands towards the tips; their eyes are dark red. Other insects (e.g., squash bugs and leaf-footed bugs) can be somewhat similar in color to BMSB, but tend to be more slender.
The immature stages of BMSB (nymphs) are smaller than adults and range from pinhead-sized to ½ inch in length. Nymphs are oval and, like adults, have dark red eyes. Nymphs vary in color, depending on their age. Initially, they are yellowish-red, but become creamy white with reddish spots just prior to turning into adults. Older juveniles have spiky projections along the sides of the body behind the head. BMSB eggs are pale, barrel-shaped, and found in clusters of 20 to 30 on the undersides of leaves. Both juveniles and adults possess tubular, needle-like mouthparts, which they use to pierce plants and feed on liquids.
Host Range
BMSB feeds on a wide range of plants. Many commercially important fruit, vegetable and field crops can be at risk, including (but not restricted to) apple, Asian pear, cherry, cranberry, currant, grape, peach, pear, raspberry, asparagus, dry bean, green bean, pepper, sweet corn, tomato, field corn and soybean. Many ornamental plants can also be attacked, including (but not restricted to) American holly, basswood, butterflybush, catalpa, cherry, dogwood, empress tree, honeysuckle, mimosa, mulberry, pyracantha, redbud, rose, serviceberry, silver maple, sweet gum, tree of heaven, and walnut.
Symptoms and Effects
Symptoms of BMSB damage can vary depending on the host plant. Damage to landscape plants tends to be minor, and the greatest threat poses by BMSB is to the fruiting structures of fruits and vegetables.
Early-season feeding on developing apples results in a surface blemish that is often referred to as “cat-facing” and makes the fruit unmarketable. Later-season feeding leads to water-soaked or necrotic (i.e., dead) areas that make the fruit more prone to invasion by rot organisms. Unfortunately, symptoms from late-season feeding may not be readily visible at the time of harvest and can while apples are in cold storage. Damage to other fruits by BMSB is similar to apples, although fruit drop may also occur. BMSB can also be a contamination issue in wine and cider production due to the pungent odor release when these insects are crushed.
On vegetables, symptoms typically include small, discolored spots, sunken areas, and distortion. On crops with seed pods (e.g., beans), pods may be discolored and individual seeds within a pod may be shrunken and fail to develop.
In addition to being a plant pest, BMSB can be a nuisance issue when adults seek out sheltered overwintering spots and invade structures in the fall. Indoors, BMSB is harmless to people and structures, but they can be a nuisance similar to boxelder bugs and multicolored Asian lady beetles. In Wisconsin, BMSB issues in structures typically involve small numbers of individuals (i.e., < 100), but in some situations, infestations can include thousands of BMSB adults. When crushed, BMSB adults release a strong odor and could also cause staining on light colored materials (e.g., curtains).
Life Cycle
In Wisconsin, BMSB has one generation per year. In warmer locations, production of a two or more generations could occur. In Wisconsin, BMSB adults overwinter in protected sites (e.g., in homes and other structures) and become active in spring. Adults mate and lay eggs from mid-spring into mid-summer. Small juveniles are often spotted in early summer with larger juveniles and new adults being spotted in mid-and-late summer.
Scouting Suggestions
Once established, BMSB populations can be highly localized. High BMSB numbers can often found near field edges, wooded edges, and in residential areas. Research to establish economic thresholds in commercial crops is ongoing, although no formal thresholds exist for home gardeners and homeowners. Likewise, research is being done to evaluate traps in commercial settings, but options for homeowners are lacking. Routine visual scouting for BMSB egg masses, juveniles (nymphs), and adults is a key approach to inform management decisions.
Management
Non-Chemical Control: For small-scale settings (e.g., home gardens, yards, and around structures) a number of non-chemical approaches can be considered. Regular scouting for eggs, juveniles, and adults, combined with squishing, hand-picking, or knocking into a container of soapy water can be a useful approach, especially if BMSB populations are low-moderate. For smaller plants that are done flowering or do not require insect pollination, floating row cover (e.g., fine mesh netting) can be considered as a physical barrier. This approach is most useful for excluding larger juveniles and adults, but small juveniles can fit through most mesh sizes. A number of beneficial insects (e.g., predators and parasites) are being studied for biocontrol purposes. Over time, some of these beneficial insects may play an important role in curbing activity of BMSB.
To prevent BMSB from invading structures in fall, an approach called physical exclusion is important. This refers to locating and sealing up potential access points on a home or other building. Common access points include gaps in siding near corners, doors, and windows, vents, access holes for pipes and wires, and similar locations. Sealing up these potential access points with caulk, expanding insulation foam, backer rod, weather stripping, or other means can help prevent BMSB adults and other pests from gaining access to a structure.
Chemical Control: A number of options exist for managing BMSB in home gardens, yards, and around structures. In home yards and gardens, a number of conventional insecticide sprays (e.g., permethrin, zeta-cypermethrin, etc.) can help protect fruits and vegetables from attack, with some residual activity. Organic options such as insecticidal soap, neem and other horticultural oils, and pyrethrins can also help, but have very short residual activity (less than a day). Luckily, pressure from BMSB has been relatively low in Wisconsin and plant damage from this insect has been relatively minor in home yards and gardens.
In large-scale and commercial plantings, growers have additional chemical control options. For management options in commercial fruit crops, see the Midwest Fruit Pest Management Guide. For management options in commercial vegetable crops, see the University of Wisconsin-Madison Division of Extension bulletin A3422 (Commercial Vegetable Production in Wisconsin).
To help prevent entry into buildings, a repellent-type insecticide (e.g., bifenthrin, cyfluthrin, cyhalothrin, deltamethrin, esfenvalerate) can be sprayed as thin bands around potential access points (e.g., edges of siding, along foundations, soffit areas). This is done in fall around or just before the time that BMSB is trying to get indoors. This same approach is used for boxelder bugs, multicolored Asian lady beetles, and other occasional invaders. Having a pest management professional treat your home can also be a consideration.
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