Guide

Look closerInsects

Western conifer seed bug: the leaf-footed bug on your window

September to April

The western conifer seed bug is a large, dull-brown bug that shows up on sunny house walls and window screens in fall while it looks for shelter from the cold, and on sunny indoor windows through winter and early spring. It is harmless to people, and the way to tell it apart is a flattened, leaf-shaped flare on each hind leg.

Why this time of year

Adults leave the pines in early fall and move toward buildings as the weather cools. Sunny walls draw them in, and they slip through gaps around windows and doors. Bugs that got inside can wake up and wander out on warm, sunny days through winter and into spring.

How to notice it

  1. On a sunny afternoon from September to November, look over the warm side of the house: siding, window frames and screens. From December on, check sunny windows indoors instead.
  2. If you spot a long, narrow brown bug, look at its back legs. A flattened, leaf-like flare on each hind leg points to a western conifer seed bug, which people often mistake for a stink bug.
  3. Look without squeezing. If one is indoors, nudge it into a cup or onto a tissue and let it go outside.
  4. Indoors in winter, check sunny windowsills on warm days, when bugs that came in last fall sometimes wake up and move around.

Try this with kids: Find a big brown bug on a sunny window and check its back legs for a little leaf. Then help a grown-up scoop it into a cup and carry it outside.

Phrase to know: “Leaf-footed bug”: a bug whose hind legs have a flat, leaf-shaped widening.

Safety

  • It does not bite or sting, but it gives off a strong smell (some describe it as piney) when handled or squashed, so move it with a cup or tissue instead of bare fingers.
  • No bug spray is needed. A cup, a tissue or a vacuum takes care of the ones that get inside.

Sources

  • massaudubon.orgMass Audubon: Massachusetts residents may see this large brown harmless home invader come fall; flattened leaf-like segment on hind legs; do not sting, bite or eat wood; pungent odor when handled; catch and release outdoors.
  • extension.umn.eduUMN Extension: attracted to sunny sides of buildings, enter through cracks around windows and doors; leaf-like hind legs; don't bite or sting; cannot reproduce indoors; bugs seen indoors in winter or spring entered the previous fall.
  • hort.extension.wisc.eduWisconsin Extension: enter buildings at the onset of cold weather; overwinter in the house; come out on warm sunny days during winter and spring; flattened leaf-like hind legs; pine-like odor; do not bite.
  • extension.colostate.eduColorado State: move to buildings September-October; harmless; do not bite; do not reproduce in the home; piney odor.
  • extension.umaine.eduUMaine: seek a warm protected place to spend the winter at the end of summer and early fall; smell when disturbed or crushed.

Checked against these sources on October 16, 2026.

In the guide for September, October, November, December, January, February, March, April

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