They're back! The first wave of invading elm seed bugs is upon us. Both adults and immatures have begun their advances on our houses. While their diet consists of elm seeds, their threat is as a nuisance home invader.
Elm seed bugs are originally from the Mediterranean area but first showed up as unwanted pests in western Colorado in 2017. Since that time they have become a well-known pest of Delta County homes. With the prevalence of seed-bearing Siberian elms, I don't expect this pest problem to disappear any time soon if ever.
Elm seed bugs have a single generation a year with adults overwintering inside buildings, wood piles, beneath tree bark, leaf litter and just about anywhere they can escape winter weather conditions. As temperatures warm up in the spring, these adults become quite active, mating and laying eggs on developing elm seeds. If only that was all they did!
When overwintering elm seed bugs emerge in the spring, they can immediately become nuisance pests. But wait -- it gets even worse. Their eggs hatch and nymphs feed on these seeds but also move around quite a bit, themselves becoming a nuisance. These nymphs feed into June before becoming winged adults. Yes I said winged! That means that they have no problem dispersing over considerable distances. So just because you don't have a Siberian elm in your neighborhood does not mean you are immune to their invasions.
Immature elm seed bugs lack wings and are smaller than their parents. As they grow, black wing pads develop and the abdomen appears as a lighter red color. Adults are the stage normally found in homes. These are about 1/3 inch long with dark, rusty-red and black coloration. The underside of the insect is red. On the back behind the head there is an upside-down black triangle set inside two rusty-red triangles.
Next to the edges of the wings are noticeable white dots interspersed with rusty-red and black dots. Wings are held crossed over the back and half of the wing is black and the other half is red and black.
Adults will be around from summer through the fall when cold temperatures drive them into protected places such as your home. High temperatures during the summer can also encourage both adults and nymphs to sneak into your home. They may enter homes via cracks and crevices, but most commonly enter via windows and doorways that have poor seals and no door sweeps. While in your home they may be seen around windows sills, walls, ceilings, furniture and behind wall hangings. When touched or squashed these bugs can give off a foul odor described as smelling like bitter almonds.
Excluding these bugs from the home is done by sealing windows and doors with weather stripping while insuring screens and door sweeps are in good condition. Ensure the caulking around windows and door frames is in good condition with no cracks. Caulk and seal gaps in soffits, gas, electrical and plumbing lines leading into the house.
Once in your home, you can vacuum up the bugs and dispose of them outside or flush down the toilet. An outside perimeter barrier of insecticide containing a pyrethroid around window and door entryways may be the best way to deter bugs entry into the home. There is nothing to be gained by spraying the side of the house or your entire landscape. Sometimes diatomaceous earth does a good enough job in reducing home invasions as a perimeter application.
Just when you thought that all that blowing seed and sprouting seedlings from Siberian elms was the worst that could happen, in walks the elm seed bug to claim victory as the top dog nuisance pest. I think I've told you before that insects rule!
Jim Leser retired to Cedaredge in 2007 after a career with Texas A&M University Extension in entomology. He is a member of the Cedaredge Tree Board and a Colorado Master Gardener.