Elm seed bugs (Arocatus melanocephalus) have found their way to Franklin County. Two occurrences were reported last year, and the first occurrence of 2020 was reported on July 2. While they are similar to box elder bugs, these insects are smaller, about 1/3 inch long. Adults have a dark, rusty-red and black coloration. On the back, there is an upside-down black triangle set inside two rusty-red triangles. Right now, the immature nymphs are only a quarter the size of adults. One of the most recognizable characteristics of elm seed bugs is their ‘busy’ habit, running around much more than their box elder bug cousins.
This year it seems adults will appear in later July and will be present until fall, congregating on plants and structures. Periods of extremely high temperatures may trigger mass migrations to seek more favorable climates inside homes during the summer. Fortunately, there is only one generation produced each year.
As nymphs and adults feed on Siberian elm seeds and leaves, using their piercing and sucking mouthparts, they cause little damage to overall tree health. After the elm seeds mature and fall off the tree the bugs become more mobile and can be found in large numbers congregating on tree trunks, the ground and on nearby structures. These insects can congregate in large numbers in soffits, around windows and under vinyl siding. With hot summer temperatures adults may congregate on the northern side of buildings or in shaded areas attempting to escape the heat. They may also be seen in the fall congregating on the southern side of structures seeking radiant heat.
It is also during the fall when the insects start to seek overwintering habitats and will often start invading homes. They may enter homes via cracks and crevices, but most commonly enter through windows and doorways that have poor seals. When aggravated these bugs give off a foul odor sometimes described as smelling like bitter almonds.
These are sheerly a nuisance pest but can be overwhelming with numbers. It is likely that these insects will increase in our area. Control can be obtained through methods similar to controlling box elder bugs. Products commonly sold for this use contain active ingredients such as beta-cyfluthrin, bifenthrin, deltamethrin, cyfluthrin, cypermethrin, lambda-cyhalothrin and permethrin. Only use products that explicitly allow for the application sites.