Box elder bugs are common insects often found near human dwellings. These insects, formally known as Boisea trivittata, are identifiable by their approximately half-inch long, black bodies with distinct red or orange markings, including three stripes behind their head and red wing edges that often form an ‘X’ shape when at rest. While generally considered nuisance pests, understanding their natural behaviors helps explain their appearance.
Natural Environment and Preferred Host Plants
Box elder bugs primarily reside in deciduous and mixed forests or open meadows, where their preferred host plants are abundant. Their main food source is the box elder tree (Acer negundo), particularly the seeds of female trees. They use piercing-sucking mouthparts to extract sap from seeds, leaves, and tender twigs for essential nutrients.
While box elder trees are their primary food source, these insects can also feed on other maple species, such as silver maples, and ash trees (Fraxinus spp.) when box elder trees are scarce. They might occasionally feed on the fruits of plum, apple, cherry, and grape trees. Despite their feeding, box elder bugs typically cause minimal damage to host plants.
Seasonal Movement Indoors
The appearance of box elder bugs indoors is a direct result of their seasonal search for shelter. As temperatures cool in autumn, these insects migrate from outdoor feeding grounds to find warm, protected places to overwinter. They are highly attracted to buildings, particularly those with southern or western exposures that receive abundant sunlight, which helps maintain their body temperature.
Box elder bugs typically enter homes through small cracks, crevices, and other openings around windows, doors, foundations, and utility penetrations. Once inside, they seek secluded areas like wall voids, attics, or behind siding to remain inactive during colder months. Box elder bugs do not seek food or reproduce indoors; their indoor presence is solely for overwintering. They are generally harmless, as they do not sting, transmit diseases, or cause structural damage, though they can stain surfaces if crushed.
Geographic Distribution
Box elder bugs are native to North America, with their distribution closely correlating with their primary host plants. The species Boisea trivittata, known as the eastern box elder bug, is found throughout the eastern United States, southern Canada, Mexico, and parts of Guatemala. Another related species, Boisea rubrolineata, or the western box elder bug, is native to the west coast of North America, from British Columbia south through California and eastward into Nevada, Utah, and New Mexico.
Their widespread presence is directly linked to the natural range of box elder trees, broadly distributed North American maples. While primarily native to these areas, Boisea trivittata has been introduced as a non-native species in other locations, such as Chile, due to ornamental maple tree planting. This demonstrates how human activities can influence their geographic spread beyond original habitats.