The October Crowd: Stink Bugs, Cluster Flies and Lady Beetles

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Four Insects, One Motive

Every October, Long Island homeowners start finding the same cast of characters on sunny walls and around windows: brown marmorated stink bugs, cluster flies, boxelder bugs and Asian lady beetles. They look unrelated and they are, but they are all doing the same thing for the same reason.

None of them is breeding indoors. None is feeding on anything in your house. They are overwintering, looking for a protected space to go dormant until spring, and your south and west facing walls are the warmest surfaces around on an October afternoon.

Which Is Which

• Brown marmorated stink bug. Shield shaped, mottled brown, with alternating light and dark bands on the antennae and the abdomen edge. Releases an unpleasant odor when crushed or vacuumed.
• Cluster fly. Slightly larger and slower than a house fly, with golden hairs on the thorax. Sluggish, and prone to appearing at a sunny window on a warm winter day. Their larvae parasitize earthworms, which is why they are worst on properties with lots of lawn.
• Boxelder bug. Black with distinct red or orange lines outlining the wings. Associated with boxelder and maple trees, and they gather in large numbers on warm walls.
• Asian lady beetle. Looks like a ladybug but varies from pale orange to deep red to nearly black, usually with a small dark M or W marking just behind the head. Unlike native ladybugs, these aggregate indoors in numbers, can leave a yellow stain, and occasionally nip.

The Timing Problem

Here is the part that determines whether anything works: these insects enter through gaps in the exterior, then move into wall voids, attics and soffits where they sit dormant. Once they are inside that void, the practical options narrow sharply. You cannot meaningfully treat a wall cavity full of dormant insects, and you would not want to, because a large number of dead insects inside a wall attracts carpet beetles and larder beetles that feed on them.

Which means the entire opportunity is the few weeks before they go in. Exterior treatment of sun-exposed walls, eaves, soffits and around window and door frames, applied in early fall, is what reduces how many get in. Applied in December it accomplishes very little.

What Actually Helps, Beyond Product

• Repair or replace failing window and door screens, and check the screens on attic and gable vents, which people forget entirely.
• Caulk gaps around window frames, door frames, and where utility lines enter the wall.
• Fit or replace door sweeps, especially on a garage service door.
• Look at the soffit returns and any gap where a roofline meets a wall. That corner is a common entry.

When They Turn Up in January

A warm winter day will wake some of them and they will emerge into the living space, usually at a window. Vacuum them rather than crushing them. Stink bugs release odor when crushed, and lady beetles can stain. Empty the vacuum outside afterward.

Do not spray the interior for them. They are not going to establish, they are not reproducing in there, and interior application for an overwintering insect that is already inside a wall is mostly wasted product in a room where your family lives.

How We Handle It

Timed exterior application in early fall on the sun-exposed elevations, with attention to the gaps these insects actually use, is the treatment that matters. It is also a good example of why a program that shuts down in October misses the point. The fall invaders arrive precisely when the seasonal trucks are being winterized.