Elm Seed Bug


seeds of the siberian elm tree

The elm seed bug is a relatively new introduced pest species in the United States that originates from the Mediterranean region of Europe. This pest was first discovered in the United States in Idaho in 2012 but has since been found in several states in the Western U.S., including Colorado, Oregon, Idaho, Wyoming and Washington, as well as farther east in Michigan. The elm seed bug primarily feeds on seeds from its host plant, the Siberian elm, but is a nuisance pest when it overwinters inside of buildings as an adult.


Elm seed bug adults are about one-third-inchlong and are mahogany and black in color. The outer edges of the abdomen have alternating black and mahogany stripes. One of the identifying features of the adult elm seed bug is a black, backwards triangle flanked by two reddish triangles on the wings. The adults are the primary life stage that is found indoors because they overwinter inside of structures. The eggs and immature stages are unlikely to be seen by homeowners.

Like other overwintering insect pests inside of structural buildings, the elm seed bug becomes a prime nuisance in the fall when they begin to migrate indoors, and in the spring, when they exit buildings to begin laying eggs and searching for their food source. They are also often seen around buildings in search of cooler air in late summer as temperatures climb above 80 degrees Fahrenheit.

The elm seed bug lifecycle consists of an egg stage, five nymphal stages, and an adult stage. Adult elm seed bugs begin to search for elm trees once they emerge from their overwintering sites and will lay eggs on the flower of elm trees. Once the eggs hatch in late April into June, they will molt through five immature stages before their final adult molt. The nymphs feed on the seed produced from elm trees and will continue their growth and development on elm trees.

Elm seed bugs do not damage elm trees or structural buildings and only are considered a nuisance when they congregate in large numbers on the sides of buildings or inside of structures during cold months. Home invasions of these pests can occur from May through September, depending on the climate and region where they have established. Although this pest has been spreading throughout the United States, government agencies have not been taking action to prevent its spread because it does not cause damage to trees and does not harm humans.

elm seed bug adult


First and foremost, a thorough inspection should be conducted inside and outside of the building to identify any possibly entry points by elm seed bugs. Small cracks and crevices that let light filter through, approximately the width of a quarter, can be large enough for elm seed bugs to enter, so these entry points should be sealed with an appropriate caulk or sealant. Larger holes and open areas around plumbing, gas or electrical conduits can be covered with fine mesh.

Spend time concentrating your inspections around doors, windows and vents where insects may easily gain access. Doors and windows should have tight seals, weather stripping, and door sweeps to help prevent pest entry. Pest proofing for elm seed bugs ultimately will help prevent entry of other pests as well, so this provides a valuable service that can be communicated to customers as extra protection. You should resist the urge to squash these pests, since they will produce a noxious odor that is quite unpleasant and may leave stains.

It is extremely difficult to completely seal out pests, so in addition to pest proofing, insecticides may be needed for managing elm seed bugs. Pyrethroid insecticides have been found to be effective at preventing entry of elm seed bugs when applied to the exterior foundation, as well as around doors, windows and roof overhangs according to label directions. If elm seed bugs do enter the home, they can be vacuumed and removed from the house to prevent further disturbance. Elm seed bugs do not reproduce indoors, so all bugs that are found inside accessed the building from outside. Homes and neighborhoods with an abundance of elm trees will be more susceptible to invasions of elm seed bugs.



Davis, Ryan S. “Elm Seed Bug.” (2017) Utah State University Fact Sheet. https://digitalcommons.usu.edu/extension_curall/1770

Maistrello, Lara, et al. “Summer raids of Arocatus melanocephalus (Heteroptera, Lygaeidae) in urban buildings in Northern Italy: Is climate change to blame?.” Journal of Thermal Biology. 31.8 (2006): 594-598.

“Elm seed bug, Arocatus melanocephalus: an Exotic Invasive Pest New to the U.S.” Idaho State Department of Agriculture. https://agri.idaho.gov/main/wpcontent/uploads/2017/09/2014_ESB_Fact_Sheet.pdf

“Rose’s VanderwWerp Identifies New Michigan Bug”. (2015) Pest Control Technology. https://www.pctonline.com/article/rose-elm-seed-bug