The Boxelder bug (Boisea trivittata) is a common North American insect recognizable by its black body marked with distinctive red or orange lines. These true bugs typically measure about half an inch long as adults and are widely distributed across the continent where their host trees grow. They are generally considered a nuisance pest rather than a threat, especially when they gather in large numbers. Boxelder bugs do not bite humans or pets, nor do they spread diseases, but their tendency to aggregate in the fall and spring makes their presence noticeable near homes.
The Required Primary Host
The primary host tree for the Boxelder bug is the Boxelder tree (Acer negundo), from which the insect gets its common name. The insects require this tree for reproduction and to sustain their developing young. Boxelder trees are dioecious, meaning individual trees produce either male or female flowers, and the bugs show a strong preference for the female (pistillate) trees.
The massive populations are directly correlated with the presence of mature, seed-bearing female Boxelder trees. The bugs feed by inserting their piercing-sucking mouthparts to extract sap. Nymphs and adults primarily target the seeds, leaves, and tender twigs of these female trees, using the seeds for growth and development.
Other Trees and Plants They Use
While the Boxelder tree is the specific host required for their life cycle, these insects will feed opportunistically on other plant species. Other trees in the Maple genus (Acer), such as silver maple (Acer saccharinum) and occasionally sugar maple, can serve as secondary feeding sites. Boxelder bugs are also sometimes found on ash trees.
Their diet can extend beyond maples and ash, especially as they move toward overwintering sites in the late summer and fall. They feed on the fruits of various orchard trees, including plum, cherry, apple, and pear. These alternate sources are not used for breeding, and large populations are rarely sustained without the primary Boxelder host nearby.
Assessing Damage to Host Trees
Boxelder bugs feed by drawing sap from the leaves and developing seeds. The damage caused by this feeding is cosmetic and rarely poses a threat to the health or longevity of a mature host tree. The primary symptom is minor leaf distortion, or slight discoloration and speckling on the foliage.
When large numbers of bugs feed on the seeds, it can cause the seed pods to shrivel or become deformed. Despite heavy infestations, the overall damage to the tree is minor, and the Boxelder bug is not classified as a destructive agricultural or landscape pest. The most significant impact of the bugs is their nuisance factor when they leave the trees to seek shelter.
Steps for Managing Tree-Based Populations
The most direct and permanent method for reducing Boxelder bug populations in a specific area is the removal of any nearby female Boxelder trees. If removing the host tree is not a practical option, managing the population can involve cultural controls that target their food source. Raking and removing the fallen seeds from the ground around the tree can eliminate a significant food supply for the nymphs.
Targeted chemical control is discouraged due to the minor damage they cause, but it may be applied to address severe nuisance issues. Insecticidal soaps or horticultural oils can be applied directly to congregations of bright red nymphs on the trunk or lower branches in the spring or early summer. A forceful stream of water from a garden hose is also effective at washing masses of nymphs and adults off the tree trunk. These measures minimize the population at its source before the adults seek overwintering sites in the fall.