Box elder bugs — the annoying visitors that swarm on the surfaces of structures by the thousands — are out in force in the fall when temperatures drop. Though they don’t cause damage to plants, structures or people, homeowners are justifiably alarmed.
Questions about the insect frequently come into Extension offices, Master Gardener plant clinics and Ask an Expert, an online information service. Here are some facts about box elder bugs.
Inside the house
For bugs inside the home, a vacuum is the easiest, safest and most reliable removal method. Many references suggest that removal of box elder trees will eliminate the insects. In fact, a tree of the same species in a neighbor’s yard, or even other maple species close by, can support the insects, too.
Their family name is misleading
Box elder bugs belong to a family called Rhopalidae, often referred to as the “scentless plant bugs.” Rhopalids are close relatives of the Coreidae, known for horrible smells emitted as warning when the insects are alarmed. The most easily recognized Coreidae are squash bugs and leaf-footed bugs.
Box elder bugs may not have as strong a scent as their smellier cousins, but they are certainly not scentless. Their unpleasant “alarm smell” is one reason vacuuming is preferable to smashing when the insects get into homes.
They are true bugs
Both Coreids and Rhopalids belong to a larger order of insects known as the Hemiptera. All Hemiptera have piercing-sucking mouthparts and outer wings that are half-leathery and half membranous, which is the origin of the order name meaning “half-wing.”
Most Hemiptera are plant feeders, including the notorious lygus, chinch and stink bugs. When entomologists refer to bugs, they are speaking not of insects in general, but members of Hemiptera.
They feed on more than box elder trees
Like the family name, the common name for this insect is misleading. Female box elder trees are the most common host plant for these bugs, but they are also found on male box elders, a few other maple species, and ash trees.
In fall, box elder bugs will feed, like stink bugs, on developing fruits like apples and pears. Numerous insects feeding on the fruit cause damage called “catfacing,” which results in lumpy and misshapen fruit. It is on fruit trees that these insects are most likely to cause actual damage.
Chemicals are not recommended
Chemical treatments for box elder bugs are rarely more effective than vacuuming. A few active ingredients are listed for the outsides of homes — these should be applied by a licensed applicator.
Again, the insects are a nuisance — their fecal pellets can stain walls or surfaces — but they do not cause structural damage or kill the trees they feed on. Large populations late in fall are typical of the life cycle of this insect. A cold winter will kill off most of the overwintering adults without chemicals.
Exclusion is the way to go
Keep box elder bugs out of homes by sealing up cracks and crevices, and repairing window screen holes and insulation. This fact sheet from the University of California, Davis, has more information on box elder bugs and their exclusion, such as removing places the insects may seek winter protection. Fewer sources of shelter in winter mean fewer insects will remain the following spring to renew the cycle.
ID is confusing
Those who have moved from the eastern part of the country may have noticed that the box elder bugs in the Northwest are different. Eastern and Western box elder bugs are two closely related species. Both types of bugs are similar to the red-shouldered bug, which is most common in the South and Southwest. To add further identity confusion, the young of all three species look almost exactly alike and have more red coloring than any of the adults.
Box elder bugs are annoying
They are certainly unwanted house guests that can require frequent vacuuming. On the other hand, brown marmorated stink bug is another similar-looking insect that comes into homes in late fall and winter.
Unlike box elder bugs, brown marmorated stink bugs have the potential to do a great deal of damage to food crops. If you think you have found brown marmorated stink bugs in your home, please check this ID fact sheet and contact the author. OSU Extension is attempting to understand the range of this pest in Oregon.
Use pesticides safely!
- Wear protective clothing and safety devices as recommended on the label. Bathe or shower after each use.
- Read the pesticide label—even if you’ve used the pesticide before. Follow closely the instructions on the label (and any other directions you have).
- Be cautious when you apply pesticides. Know your legal responsibility as a pesticide applicator. You may be liable for injury or damage resulting from pesticide use.
