Milkweed bugs, scientifically known as Oncopeltus fasciatus, are common insects often found on milkweed plants. These brightly colored true bugs are a familiar sight in gardens and natural areas across North America. Their distinctive orange and black patterns serve as a warning to potential predators.
The Primary Diet of Milkweed Bugs
Milkweed bugs primarily feed on the seeds of milkweed plants. This diet provides necessary nutrients for their growth and reproduction. They are equipped with piercing-sucking mouthparts, which they insert into the milkweed seeds to extract the contents. The bugs inject digestive enzymes into the plant tissue, liquefying the material before consuming it.
They prefer seeds within the pods of various milkweed species. Common milkweed (Asclepias syriaca) and swamp milkweed (Asclepias incarnata) are among their preferred host plants. Nymphs feed exclusively on milkweed seeds; adults also rely on them. Their feeding method typically targets the outer layers of seeds within a pod, often leaving many interior seeds intact.
Occasional and Alternative Food Sources
While milkweed seeds form the bulk of their diet, milkweed bugs can consume other food sources, especially when seeds are scarce. They may feed on other parts of the milkweed plant, including young leaves, stems, and flowers. Adults also feed on nectar from various flowers.
When milkweed is unavailable, adult milkweed bugs can feed on seeds from other plants, such as sunflower and watermelon. Small milkweed bugs (Lygaeus kalmii), a closely related species, are also known to consume nectar and, opportunistically, other insects like monarch caterpillars, pupae, or aphids when their primary food is limited. These alternative food sources are secondary and do not support their growth and reproduction as effectively as milkweed seeds.
How Their Diet Impacts Plants and Ecosystems
Milkweed bugs do not cause significant harm to milkweed plants or their ability to reproduce, despite feeding on seeds. Their feeding habits leave enough seeds viable for the plant to propagate. Large populations may stress a plant, leading to some misshapen seeds or reduced seed production.
These insects are part of the natural ecosystem and are not viewed as pests requiring control. Their presence helps manage milkweed populations by consuming some seeds, which can be beneficial in areas where milkweed might otherwise grow excessively. Milkweed bugs also serve as a food source for other animals in the ecosystem.