Brown marmorated stink bug or western conifer seed bug?
These two get mixed up often. Both are rated Harmless, but they behave differently, so knowing which one you have still helps.
Why people mix them up
Both are brown, about 5/8 to 3/4 inch long and move into houses in the fall in large numbers. They show up on the same sunny walls and window frames, often side by side.
Look at the shape and the back legs. The brown marmorated stink bug is a wide shield with banded antennae. The western conifer seed bug is long and narrow, with a flat leaf-shaped flare on each back leg and a thin white zigzag across its back. Neither one bites or stings.
Brown marmorated stink bug
Photo: Emmett Collins-Sussman, CC BY 4.0, via iNaturalist
Size: about 17 mm (about 5/8 inch) long
- Shield-shaped, mottled brown to gray-brown bug
- Antennae with alternating light and dark bands (look for a pale band near the tip)
- Edges of the abdomen, sticking out past the wings, banded light and dark
- Smooth, rounded shoulders with no spines or teeth
- Gives off a strong odor when handled or crushed
It does not bite or spread disease; it just smells bad when crushed and can show up indoors in large numbers.
Western conifer seed bug
Photo: Gavin Slater, CC BY 4.0, via iNaturalist
Size: about 16–20 mm (5/8 to 3/4 inch) long
- Long, narrow reddish-brown to dark brown bug
- Back legs have a flat, leaf-shaped flare partway down
- Thin zigzag white line across the middle of the back
- Yellow-orange and black patches on the abdomen, mostly seen when it flies
- Slow-moving; buzzes loudly when it flies
This big, slow bug looks alarming but does not bite people, spread disease or damage the house; it may give off a piney smell if handled.
How to tell them apart
- The seed bug is long and narrow rather than shield-shaped, and its back legs have a flat, leaf-like flare.
- The stink bug is broad and shield-shaped with banded antennae, not long and narrow with flared back legs.
Still not sure? Use the picker, and if a bite worries you, call Poison Help at 1-800-222-1222.