Large Milkweed Bug

Large milkweed bug adult with rostrum tucked under body

Rio Salado Habitat Restoration Area, 2439 S. Central Ave. Phoenix, AZ

Large milkweed bug Oncopeltus fasciatus, hemipteran (true bug), Lygaeidae family. Found in disturbed areas and open pastures from Costa Rica to southern Canada. It is hemimetabolous with four nymphal stages in a month before molting to adulthood. The nymphs have inchoate wings.

Northern populations are highly migratory correlating to flowering of milkweeds. Tropical populations move shorter distances due to abundant resources.

To feed, they inject saliva into a milkweed follicle through their long rostrums (seen in image above), to pre-digest the seed so they can suck it up through their anterior pump and pharynx.

Their color is an aposematic warning that they sequester toxic milkweed compounds and are noxious to predators. O. fasciatus exhibits Müllerian mimicry- a defense mechanism of different species with mutual predators.

They are desirable lab organisms due to being easy to rear and handle, short developmental time, few instars, and high fecundity.

Large Milkweed Bug nymphs of varying instars