07/08/2026
It's that time of year and elm seed bugs are wreaking havoc all around the Treasure Valley. They are a common nuisance throughout the valley.
Here are the key facts about them:
They are native to the Mediterranean region and southern Europe.
First detected in the United States in 2009 in Ada and Canyon counties. They have since spread statewide here in Idaho and to other parts of the Pacific Northwest and Intermountain West, wherever elm trees are present.
-Adults are small, about 1/3 inch long.
-Dark chocolate-brown to black with rusty-red highlights.
-Distinctive upside-down black triangle on the back, set within rusty-red markings.
-Wings crossed over the back; reddish/orange abdomen visible from below or when flying.
-Nymphs are smaller, brighter red with dark heads, turning mottled pink-tan as they mature.
-They are often confused with boxelder bugs and cockroaches but are smaller and have different markings.
-They have one generation per year.
-Overwinter as adults in homes, wall voids, under bark, leaf litter, or protected spots.
-In spring, they move to elm trees, mate, and lay eggs on seeds/flowers.
-Nymphs feed on elm seeds (May–June); adults appear in early–mid summer.
-They are highly active crawlers and fliers.
-Seek shelter in buildings during hot summer weather (July–August) to escape heat and again in fall to overwinter.
-No damage to trees, buildings, or people. They do not bite or sting.
-Primarily a nuisance pest when they congregate in large numbers on sunny walls (especially north side in summer, south side in fall) and enter homes.
-Emit a foul, citrusy, odor when crushed or disturbed.
Prevention tips:
-Seal cracks around windows, doors, foundations, and utility entries. Use weatherstripping and repair screens.
-Vacuum them up instead of crushing.
-Rake and remove fallen elm seeds in late spring/early summer to reduce food for nymphs.
-Exterior perimeter insecticide treatments will help as a barrier during peak season.
-Our professional pest control treatment is popular for recurring issues.
Elm seed bugs are now well-established in Boise and tend to be more noticeable in neighborhoods with mature elm trees. While harmless, their sheer numbers can be frustrating during hot spells or in the fall.
If you're dealing with them at home, let us know. We'll be glad to help keep them at bay.