Box elder bugs are a common insect often encountered around homes, particularly as seasons change. They are primarily considered a nuisance due to their tendency to gather in large numbers. While they frequently congregate on building exteriors, they may also seek shelter inside.
Identifying Box Elder Bugs
Adult box elder bugs are about one-half inch long. They are predominantly black with red or orange markings. These markings include three longitudinal stripes on their prothorax and red borders on the basal part of their wings. When at rest, their wings lie flat, often overlapping to form an “X” shape. Their abdomen is bright red.
Young box elder bugs, called nymphs, differ from adults. They are smaller and almost entirely bright red, lacking developed wings and distinct black markings. As nymphs mature, their legs, antennae, and developing wing pads gradually darken to black. Fully grown nymphs are approximately one-sixteenth of an inch long. Eggs are small, reddish ovals found in clusters on host trees.
Where Box Elder Bugs Live and What They Eat
Box elder bugs are native to North America and are commonly found wherever their primary host trees, box elder trees (Acer negundo), grow. They also feed on other trees within the maple family, such as silver maples, and occasionally ash trees. They primarily consume sap from the leaves, tender twigs, and developing seeds of these trees. They use specialized mouthparts to pierce plant tissues and draw out the sugary fluids.
Their life cycle begins in spring when overwintered adult females lay reddish-brown eggs in bark crevices or on the leaves of host trees. These eggs hatch in 11 to 14 days, giving rise to nymphs that feed and develop throughout the summer. In the fall, adult box elder bugs seek sheltered locations to overwinter, often congregating in large numbers on sunny surfaces, including building sides. They do not reproduce indoors, but emerge from their hiding spots in spring to return outdoors and continue their life cycle.
Are Box Elder Bugs Harmful?
Box elder bugs are generally considered nuisance pests rather than a significant threat to humans, pets, or property. They do not sting and are not known to transmit diseases. While their mouthparts are designed for piercing plant tissues, they rarely bite humans. In the uncommon event of a defensive bite, it may result in a minor, irritating red mark similar to a mosquito bite, but it is not harmful. Pets that consume box elder bugs might experience an unpleasant taste, potentially leading to vomiting, but they are not poisonous to them.
They typically do not cause structural damage to homes. However, their presence in large numbers can be bothersome, and they can occasionally stain light-colored surfaces, such as curtains or walls, with their feces or when crushed. Damage to host plants is usually minor and cosmetic, such as slight leaf discoloration or deformities in fruit, and does not seriously harm the plant’s overall health.
Preventing Box Elder Bug Invasions
The most effective way to manage box elder bugs is to prevent them from entering structures. Sealing potential entry points around the home is a primary strategy. This involves repairing or replacing damaged window and door screens and ensuring screens are present on roof and soffit vents.
Sealing cracks and crevices around doors, windows, foundations, and where different materials meet, such as brick and wood siding, can significantly reduce the number of bugs entering. For long-term control, particularly for properties with significant infestations, removing female box elder trees near the home may be considered, as these trees are their primary food source and breeding ground. If trees cannot be removed, clearing fallen seeds from beneath them can help.