Box Elder Bugs and Cluster Flies

Box elder bugs and cluster flies both do the same thing every autumn for the same reason: they are looking for somewhere to overwinter, and a sun-warmed wall on the south or west side of a house looks like a good option. Box elder bugs cluster in visible masses and can leave a stain if crushed against fabric or paint, but they do not bite or damage the structure. Cluster flies behave similarly but tend to work their way into wall voids and attics, showing up sluggishly on warm days through the winter.

Because neither pest is dangerous, the response is mostly about reducing next year's numbers rather than an emergency treatment this week. Sealing the gaps they use to get behind siding and into attic spaces does more for the long run than anything sprayed after the fact — though a licensed applicator's exterior treatment, timed just ahead of when they typically mass, meaningfully cuts down how many make it that far.

What this usually involves

• Timed treatment of south- and west-facing walls before they mass
• Exclusion recommendations to reduce next year's numbers
• Cluster fly treatment around eaves and attic vents
• Help telling a nuisance invader from something that needs more attention

Get Matched With a Pest Control Company