Large milkweed bugs (Hemiptera: Lygaeidae: Oncopeltus fasciatus) are often found on (surprise!) milkweed plants. The individuals above were mating on the flower head of a swamp milkweed (Asclepias incarnata, Asclepiadaceae) in a southeast Michigan floodplain forest.
As members of the seed bug family (Lygaeidae), these bugs feed primarily on milkweed seeds. Like monarch butterflies, these bugs ingest toxins from the milkweed plant that make them poisonous to would-be predators. Also like monarchs, their bold color pattern serves as a warning of this toxicity.