Stink Bugs

Stink bugs are shield-shaped insects that feed on plant juices and release a strong, cilantro-like odor when crushed or threatened. The one invading US houses each fall is the brown marmorated stink bug, an invasive species from Asia; it doesn't bite, sting or damage homes, but it can gather by the hundreds in walls and attics.

How to recognize a stink bug

• Shield shape, about 5/8 inch long and nearly as wide.
• Triangular plate (scutellum) in the middle of the back.
• Piercing beak folded under the head.
• Six legs, two antennae with five segments.

The brown marmorated stink bug (BMSB) specifically has (per Penn State and UMD Extension):

• mottled brown-gray, "marbled" upper surface, 14–17 mm long;
• light bands on the last two antenna segments;
• alternating dark and light bands along the exposed edges of the abdomen;
• dark bands on the wing tips and small coppery or bluish metallic pits on the head and "shoulders";
• smooth (not toothed) front edge of the shoulders.

Types of stink bugs in the US

Bugs similar to stink bugs

Where stink bugs come from

BMSB was first collected in Allentown, Pennsylvania, in 1998, though Penn State believes it arrived a few years earlier, probably in shipping material from China, Japan or Korea. It has spread across the Mid-Atlantic, Midwest, South and West Coast. The worst crop damage has been in the Mid-Atlantic, and home invasions are heaviest in Pennsylvania, Maryland, Virginia, West Virginia, New Jersey and the Portland, Oregon area.

Where do stink bugs come from in your house? They don't breed indoors. In September and October adults fly to warm, sunny walls and crawl into cracks around windows, siding, soffits, chimneys and attic vents. They spend winter dormant inside walls and attics. On warm winter and early spring days some wake up and, trying to get back outside, wander into living space. Penn State notes they typically emerge from gaps behind baseboards, around window and door trim, and around ceiling lights and exhaust fans. That's why you find them in January, and why many die on windowsills.

What do stink bugs eat?

They pierce plants and suck the juice. BMSB feeds on a very long host list: apples, peaches, apricots, figs, pears, citrus, tomatoes, peppers, sweet corn, soybeans, beans, okra, grapes, and ornamentals like butterfly bush, catalpa and honeysuckle. Feeding on apples causes dimpled "cat facing," on tomatoes and peppers spongy areas inside the fruit, and on beans scarred, deformed pods.

Indoors they don't feed at all; overwintering adults live on fat reserves. They won't touch your pantry food or houseplants in any meaningful way.

Some native stink bugs, like the spined soldier bug, are predators of caterpillars and beetle larvae and are garden allies.

Life cycle and how long they live

• Eggs: light green to yellowish, barrel-shaped, glued side by side in masses of 20 to 30 on leaf undersides, May through August.
• Nymphs (baby stink bugs): five stages, 2.4 mm to 12 mm. Newly hatched ones are round, black and red; older ones are dark with off-white and reddish markings. No wings.
• Adults appear in midsummer. Pennsylvania usually gets one generation a year; warm years and southern states can get two.
• Overwintering: adults seek shelter September to October, emerge late April to mid-May.

Adults that overwinter live roughly 6 to 8 months in total.

Can stink bugs fly?

Yes. Adults are strong fliers and often fly into lights and lamps, buzzing loudly. Nymphs can only crawl. Bugs that land on screens or clothes also ride indoors when you open the door.

Do stink bugs actually stink?

The smell is a defense. When crushed, handled, vacuumed or even roughly disturbed, they release liquid from scent glands. Most people compare it to cilantro, coriander or old socks. Halogen lamps that cook them produce a burning smell. The odor lingers on curtains, clothes and inside vacuums, which is the main reason people learn quickly not to squash them.

Are stink bugs dangerous?

• To people: no bites, no stings, no disease. Penn State lists two minor health effects: the odor chemicals can act as an airborne allergen (rhinitis, conjunctivitis) for sensitive people, especially those who also react to cockroaches or lady beetles, and crushing one on bare skin can cause local dermatitis. Rinse with soap and water; see a doctor if eye or breathing symptoms persist.
• To pets: eating one usually causes drooling or vomiting because of the taste. Many at once can upset the stomach; call your vet if vomiting continues.
• To the house: no structural damage and no breeding indoors; they can spot curtains and walls with droppings.
• To gardens and farms: significant damage to fruit and vegetables.

What people who dealt with them say

Threads in r/pestcontrol and r/homeowners tell a very consistent story:

• "They just showed up one year." Infestations often start suddenly as BMSB reaches a new area, and the same window or the same sunny side of the house gets hit every fall.
• Late winter is the worst indoor season for many people: 5 to 20 bugs a day on warm days, often in one room, near a fireplace or coming out of recessed can lights. Several people found them living in the chimney.
• Even tight houses get them. Owners of new and spray-foamed homes still report a few a day. New windows helped noticeably for some.
• Pros are blunt: you won't eliminate them, you can reduce them. One technician described cutting sightings by over 90% with fall exterior treatments focused on attic vents, but said it usually took about six months to see the difference, because the bugs already in the walls keep trickling out.
• What people actually use: a cheap dedicated hand vac, a jar of soapy water, or the toilet. Crushing and the main household vacuum get abandoned after one bad smell.
• Beware upsells. One Portland homeowner was quoted $7,000 to replace attic insulation for stink bugs; pros in the thread called it a rip-off and said insulation rarely needs replacing.

How to deal with them

The short version, detailed in how to get rid of stink bugs:

1. Seal gaps around windows, siding, vents and utility lines before September.
2. Remove indoor bugs into soapy water or with a dedicated vacuum.
3. Trap winter wanderers with a pan of soapy water under a lamp, the design that won a Virginia Tech homeowner trial.
4. Don't crush them, and skip indoor bug bombs; they don't reach bugs in walls.