Boxelder Bugs Without Boxelder Trees?

Q. I found 50 to 100 of red and black beetles running around the rocks in my yard while I was pulling weeds. If these numbers are representative, I must have thousands. A friend thinks they may be Boxelder Bugs but I don’t have any Boxelder trees in my yard. The pictures of Boxelder Bugs online are similar but do not look exactly like these. So what are they and should I declare war on them and begin spraying?

Western boxelder bug

A. I was confused at first when I first saw these same bugs because I also thought they were Boxelder Bugs. But they acted differently from those back East. In fact, they are Boxelder Bugs. There are Eastern and Western Boxelder bugs. They look similar but are slightly different from each other.

            In the East these critters prefer trees like Boxelder, Maple and Ash. There they are more of a nuisance to homeowners than a problem. In the Western United States, they are thought of the same way; more of a nuisance than a problem. But they can pose a problem with fruit trees and in backyard orchards if their numbers are high enough.

            Here they may feed and associate with ash trees in landscapes but we see them in backyard orchards as well, particularly if mulch, either wood or rock, is used to cover the soil surface. They stay alive during the winter by finding some cozy place to congregate in the mulch when it is cold. It is here they “hibernate” until warm weather and food reappears.

            They can be a nuisance in fruit trees, and possibly damage young and older fruit, by their feeding. They feed on plants the same way as squash bugs, leaf footed plant bugs and stinkbugs. They suck plant juices out of soft tissues, leaf and fruit (the softer the better), with a long hypodermic needle-like mouthpart. Seems awkward to have but they tuck it across their belly when it's not being used.

            When they find leaves or immature fruit for feeding they pull out it out like a drilling rig and stick it in soft leaves or fruit. The feeding punctures and damages soft plant tissue. Sometimes it can be responsible for some disease problems. Expanding leaves become deformed and fruits dimpled as they grow. If the attack is severe or the attacked part very young, the leaf or fruit may drop from the plant.

            Their damage is most noticeable in pears, apples, plums, peaches and almonds. They normally don't create noticeable damage to ornamental trees or shrubs so we ignore them. Spraying chemicals is not worth the benefit or environmental trade-off unless their levels are sufficiently high and the damage is causing problems.