a box elder bug rests inside in a sunny patch

Bug of the Month: Box Elder Bugs

Have you ever seen a small black bug with red on its back hanging out around your house during spring or fall? Chances are that it’s a box elder Bug, whose name comes from its nature of living in, and outside of, box elder trees. The most common time you will find box elder bugs is during spring and fall, as they leave and enter your home to overwinter.


Adults are about ½” long, and have black with orange or red markings on the flat wings on their back. There are three stripes on the thorax, which is the area directly behind the head. Infant box elders are called nymphs, and measure only around 1/16” long, with a bright red color. It isn’t until they grow older that the black becomes prominent on their skin.


The Latin name for box elder bugs is Boisea trivitta. Its namesake comes from its nature of nesting in box elder trees, but they are also found on maple and ash trees. They lay eggs on trunk branches and leaves of the trees, and rarely will you find them on a male box elder tree. As weather cools, they begin to move into homes to overwinter, which is why homeowners typically see them in spring and fall. They only live a few days or weeks and they often live within the walls.

What Do Box Elder Bugs Eat?

During Spring, box elders will emerge from their overwintering sites and begin to feed on low vegetation and seed on the ground. A couple weeks later, and starting in July, they will move on to consuming female, seed bearing box elder trees. Their feeding does not cause injury to these trees, but during high population season in the summer, you may find their young on the ground or in the garden feeding. They can definitely be a damaging pest to homes and gardens!

In the Home

They are attracted to homes with a sunny exposure and warm areas, with large western or southern exposure to the sun. Usually, you will start to see them around the windows and doors at the beginning of winter when weather is still mild, and again as spring starts in full effect; then returning again in fall to repeat the process.

Find more about other insects on the Bug of the Month section of our blog.