Insects with bold red and black markings often prompt concern from homeowners. This distinct coloration, known as aposematism, serves as a warning signal to predators that the insect is toxic, tastes foul, or has another defense mechanism. While this striking color combination is common, a few species are responsible for the majority of sightings around homes in North America and Europe. Identifying these insects based on their appearance and behavior is the first step toward understanding their role in the local environment.
The Most Common Culprits
The Box Elder Bug (Boisea trivittata) is one of the most frequent visitors, often aggregating on the sunny sides of buildings in the fall. This true bug is approximately one-half inch long with a flattened, elongated oval body. Its coloration is black, accented by bright reddish-orange lines along the edges of the forewings and three distinct stripes behind the head. When the wings are folded flat, the markings often overlap to form a noticeable ‘X’ shape.
The Large Milkweed Bug (Oncopeltus fasciatus) is slightly more slender, ranging from one-half to one inch long. Its body is primarily reddish-orange with black patches on the wings and a black band across the middle of the back. This species is almost always observed on milkweed plants, where it uses piercing-sucking mouthparts to feed on the seeds.
Lady Beetles, commonly called Ladybugs, are the third group of red and black insects. These insects are easily recognizable by their small, dome-shaped, and rounded bodies, typically ranging from a quarter-inch to a half-inch long. The most common species are often red or orange with varying numbers of black spots, or occasionally black with red or yellow markings.
Distinguishing Features for Identification
Identifying a red and black insect requires observing its body structure, particularly the wings, to distinguish between a true bug and a beetle. True bugs, such as the Box Elder Bug and Milkweed Bug, have forewings that are partially hardened near the base and membranous at the tips. This structure results in the wings crossing over the back to create an ‘X’ or a triangular shape.
Beetles, like Lady Beetles, possess hardened shell-like forewings called elytra that meet in a straight line down the center of the back. True bugs and beetles also differ in mouthparts: true bugs have a proboscis for piercing and sucking fluids, while beetles have mandibles for chewing. Location provides further clues, as Milkweed Bugs rarely stray from their host plant, while Box Elder Bugs congregate on warm walls in the autumn.
Are They Pests or Helpers
The ecological role of these brightly colored insects falls into the categories of beneficial, harmless, or nuisance. Lady Beetles are considered beneficial insects in gardens because both the larvae and adults are voracious predators of soft-bodied pests like aphids and scale insects. They contribute to natural pest control by consuming large quantities of these plant-damaging insects.
The Large Milkweed Bug is considered harmless to most plants, as its diet focuses on milkweed seeds and it does not feed on garden vegetables. Box Elder Bugs are categorized as nuisance pests because their feeding on tree sap causes little lasting damage to host trees. They are a nuisance primarily due to their habit of gathering in large numbers on buildings and entering homes to seek winter shelter.
Dealing with Common Infestations
Management strategies should be tailored to the insect’s ecological status, focusing on controlling nuisance species. No control is necessary for beneficial Lady Beetles and harmless Milkweed Bugs, and they should be left to perform their natural functions. Control efforts are reserved for Box Elder Bugs when they become problematic by invading structures in the fall.
The most effective approach for managing Box Elder Bugs is exclusion, which involves identifying and sealing entry points on the exterior of the home before the insects move indoors. This includes using caulk to seal cracks around windows, utility lines, and foundations, and ensuring window screens and door sweeps are intact. If insects have already entered, mechanical removal using a vacuum cleaner is the preferred method, as crushing them can release a foul odor and stain surfaces.