The Boxelder bug (Boisea trivittata) is a common nuisance insect found across North America, often becoming noticeable when it congregates around homes in the fall. These black and red insects are primarily outdoor pests associated with certain trees. Boxelder bugs generally do not bite humans or pets because their feeding apparatus is not designed for that purpose. They pose no threat of injecting venom or transmitting diseases to people.
The Definitive Answer: Biting Behavior
Boxelder bugs are classified as “true bugs” (order Hemiptera), meaning they possess specialized mouthparts called a rostrum. This structure is a tube-like piercing-sucking apparatus designed specifically to extract fluids from plants. Their natural diet consists of the seeds, leaves, and flowers of host trees, primarily the female Boxelder tree, as well as certain maple and ash varieties.
These mouthparts are not adapted for feeding on mammalian blood or tissue. They lack the intent or biological mechanism required to puncture skin and draw a meal, unlike mosquitoes or fleas. If a person reports a sensation from a Boxelder bug, it is likely a defensive reaction.
A mild, temporary “prick” may occur if a bug is trapped against the skin or roughly squeezed. In this rare scenario, the insect may use its rostrum defensively, causing a slight irritation or a temporary red mark. This action carries no known risk of disease transmission or significant harm.
Identifying Boxelder Bugs
Adult Boxelder bugs are slender, dark brown to black insects, measuring around one-half inch in length. They are easily recognized by the striking reddish-orange markings that outline the edges of their wings and abdomen. A distinctive feature is the three vertical reddish-orange lines on the area directly behind the head.
The younger Boxelder bugs, known as nymphs, look similar in shape but are smaller and brighter. Nymphs are predominantly a vibrant reddish-orange color, lacking the full black wings of the adults. All stages of the insect are commonly found near their preferred host trees, which include Boxelder, maple, and ash.
Why They Are Considered Pests
Boxelder bugs are considered nuisance pests because of their large numbers and overwintering habits. They do not cause structural damage to homes or significant harm to mature trees. The primary problem begins in the fall when the weather cools and they congregate.
They seek out sunny, warm areas, often clustering on the south and west-facing walls of buildings to absorb heat. This aggregation behavior leads them to find small gaps and cracks to move inside homes, seeking a protected place to spend the winter. Once indoors, they remain largely inactive, but their presence is unwelcome.
The most frustrating consequence of a Boxelder bug invasion is the mess they create when handled. When crushed, the insects release a mildly unpleasant odor and can leave behind a reddish-orange stain. Their excrement can also stain curtains, carpets, and walls, causing discoloration on light-colored surfaces.
Managing Aggregation and Entry
The most effective strategy for managing Boxelder bugs is home exclusion, achieved by sealing all potential entry points before the insects begin their fall migration. This involves using caulk to seal cracks and crevices around window frames, door casings, and utility pipes entering the house.
Any damaged window or door screens should be repaired, and weather stripping should be installed under exterior doors. For outdoor clusters, a simple, non-chemical control involves spraying the groups with a forceful stream of water from a garden hose. A mixture of liquid dish soap and water can also be sprayed directly onto the bugs, which helps to break down their protective outer layer.