Identification
Adult: overall black and orange - leathery portion of forewing with orange forward-pointing triangle anteriorly, and orange backward-pointing triangle posteriorly, separated by a black band in the middle; membranous portion of forewing black; pronotum black with orange lateral margins; freshly-molted young adults are very pale yellow, their color becoming darker and more orangish with age; adult males have a black band on the ventral side of the fourth abdominal segment; adult females have two black spots in that location
Nymph: early instars have a bright orange abdomen, developing black spots with age; later instars are more orangish-yellow; pronotum orange with black posterior margin; wingpads black, lengthening with age
Egg: oblong with three downcurved projections at tip; color initially yellow, changing to orange and then bright red before hatching
Range
eastern and southwestern United States, plus Ontario; most common in southeast
Habitat
Fields and meadows containing milkweed or dogbane
Season
May-October (North Carolina)
Food
Seeds of milkweed plants. Adults sometimes take nectar (and other plant juices).
Life Cycle
Eggs are laid in milkweed seed pods or in crevices between pods. About 30 eggs are laid a day, and about 2,000 over a female's lifespan, which lasts about a month during the summer. One or more generations per year. Adults overwinter.
Remarks
In the course of feeding these bugs accumulate toxins from the milkweed, which can potentially sicken any predators foolish enough to ignore the bright colors which warn of their toxicity.
See Also
Adults of the
Small Milkweed Bug (
Lygaeus kalmii) have a red "X" marking on the forewing, and a red transverse band on the pronotum, not orange lateral margins.
Small Milkweed Bug nymphs are more red than Oncopeltus nymphs, and have two diagonal black markings on the pronotum.
Adults of the
Eastern Boxelder Bug (
Boisea trivittata) and the
Western Boxelder Bug (
Boisea rubrolineatus) lack triangular orange patches on the forewing.
In the far south, other species of
Oncopeltus such as the
Six-spotted Milkweed Bug (
O. sexmaculatus) have two large orange patches on the pronotum, whereas only the lateral margins of the pronotum are orange in the Large Milkweed Bug
Print References
Arnett, p. 258, fig. 20.27--mislabeled
Lygaeus (2)
Milne, p. 479, fig. 115
(3)
Swan and Papp, p. 125, fig. 115
(6)
Slater, p. 71, fig. 119
(7)Internet References
live adult and nymph image plus biology and rearing information (U. of Illinois at Urbana-Champaign)
live adult and nymph images plus foodplant and other info (Bruce Marlin, Illinois)
live adult image of pair mating (Georgetown U., Washington DC)
live adult and nymph images (Randy Newman, North Carolina)
live adult image (Bastiaan Drees, Texas A&M U.)
live adult image (David Cappaert, forestryimages.org)
photo of eggs and microscope photos and capition of oogenesis (Cassandra Extavour, U. of Cambridge, UK)
