Visual characteristics like color patterns are often the first clues for identifying insects. Many species share markings like black bodies with red stripes, but differ in other ways. This article clarifies the identities of common black bugs with red stripes, providing details to differentiate them.
Common Black Bugs with Red Stripes
Several insect species display a black and red striped pattern, often serving as a warning to predators. Common examples include the Large Milkweed Bug, Small Milkweed Bug, and Boxelder Bug, each with distinct features.
The Large Milkweed Bug ( Oncopeltus fasciatus ) measures about 11 to 12 mm in length. Its forewings feature a striking pattern with an orange, front-pointing triangle, a wide black band, and an orange backward-pointing triangle. The outer, membranous portion of the forewing is black, and its pronotum (the shield-like plate behind the head) has a black, forward-pointing triangle bordered by orange. These bugs are commonly found on milkweed plants, where they feed on seeds, leaves, and stems using their piercing-sucking mouthparts.
The Small Milkweed Bug ( Lygaeus kalmii ) measures 10 to 12 mm long, generally smaller than its large counterpart. Its distinct orange-and-black pattern often forms a reddish-orange “X” shape on its back that does not quite meet in the middle. This species also has a reddish-orange band across its pronotum, sometimes with two black spots on the front edge and two black half-circles on the hind edge. Small Milkweed Bugs inhabit fields and meadows, primarily feeding on milkweed seeds and nectar, though adults may scavenge or prey on other insects when milkweed is scarce.
The Boxelder Bug ( Boisea trivittata ) is identifiable by its black body, approximately 1/2 inch long, adorned with reddish or orange markings. It has three prominent red lines on its thorax and a red line along each side of its body. When its wings are at rest, they lie flat over the body, often forming an “X” or inverted “V” shape due to the overlapping red-veined patterns. Boxelder bugs are typically found near boxelder trees, maple trees, and ash trees, feeding on seeds and newly developing leaves.
Are These Bugs Harmful or Helpful?
The impact of these black and red striped bugs on humans and the environment varies by species.
Large Milkweed Bugs are harmless to humans and pets, as they do not bite or sting. They are not agricultural pests and do not significantly damage milkweed plants, their primary food source. While they feed on milkweed seeds, they leave enough resources for plants to thrive. These bugs also help control milkweed populations and serve as food for other animals.
Small Milkweed Bugs are also harmless to humans and do not bite or sting. While they feed on milkweed seeds and occasionally other insects, their presence does not pose a threat to gardens or plants. Their feeding habits on milkweed seeds help regulate plant growth as part of the natural ecosystem. Both large and small milkweed bugs sequester toxins from milkweed, making them distasteful to predators, indicated by their bright coloration.
Boxelder Bugs are nuisance pests rather than harmful ones. They do not bite or sting humans. They rarely cause significant damage to the trees they feed on, such as boxelder, maple, or ash, and are not agricultural pests. Boxelder bugs often congregate in large numbers on the sunny sides of buildings in the fall, seeking winter shelter, and may enter homes through small cracks and crevices. While they do not cause structural damage, they can leave stains on surfaces if crushed.