Physical Characteristics

The adult western boxelder bug is around 1/2 inch long, and about a third that in width. Its topside is grayish-black and has several reddish lines running across it, including an “X” figure, with the legs of the “X” forming the top border of a darker portion. Its pronotum (the cowl-like area behind its head) is bisected by a vertical line, and there are two additional lines, one on each side of the pronotum. Its abdomen is red, and young nymphs are all red, with darker color developing through successive molts. Its antennae are long and curving.


Western Boxelder Bug


Boxelder bugs usually feed on the leaves, flowers and helicopter-like seedpods of the female box elder tree (Acer negundo), but they also like maple and ash trees, and occasionally will dine on almonds, apples, cherries, peaches, pears and plums when those fruits and nuts are still on the tree, and also on grapes. This insect is a true bug with an elongated sucking proboscis, and its puncture points damage fruit and nuts. As a household pest, the western boxelder bug is more of a nuisance than a menace, and it achieves that status by sheer numbers in the fall and spring, when throngs of these bugs invade patios or get inside houses, where they can spot curtains, furniture and clothing with their excrement.   


If you’re experiencing an infestation of western boxelder bugs, the first thing you want to focus on is exclusion, or keeping the bugs out of your house. Examine window screens and replace torn ones, and close up entry points where the bugs can enter with caulking, weatherstripping, steel wool, fine-mesh screening or expandable foam. If the bugs already are inside, vacuum them up or collect them by hand. Outside, get rid of hiding places – boards, leaves, debris and piles of rocks – where the western boxelder bug finds shelter to overwinter. Rake leaves and remove weeds in a six- to 10-foot perimeter around your house, especially on the south and west faces. Clusters of bugs on walls and fences can be removed by power-spraying water. You may want to consider removing any box elder trees (Acer negundo), which provide the primary food for this insect. Your Clark Pest Control technician should be a source for good advice on exclusion strategies to keep the western boxelder bug outside of your living space.