Monarch butterflies depend on milkweed to survive–but they’re not the only ones!
There are two true bugs that are associated with milkweed at this time of year, the large milkweed bug (Oncopeltus fasciatus, pictured) and the small milkweed bug. (The designation “large” is relative, as this little insect is only about ¾ ” long!) Both are strikingly colored in red and black, and feed exclusively on the sap and seeds of plants in the milkweed (Asclepias) family. Although they’ll feed on any part of the plant, their preference is for the seeds, and large gatherings of all life stages can be seen on milkweed plants in late summer and early fall.
Like all true bugs, they have sucking mouthparts which inject digestive enzymes into the plant tissue, slurping up the resulting ‘milkweed smoothie’ through their straw-like beak. (Because of the length of these mouthparts, they can reach only the outside layers of seeds in each pod, so plenty of interior seeds are left intact.)
Females lay pale yellow eggs in the crevices between the seed pods–up to 30 eggs a day–for about a month. The eggs change to a bright orange/red before the nymphs hatch in a few days. They remain together, feeding en masse on developing seeds, although they’ll scatter if disturbed.
Like monarchs, both large and small milkweed bugs sequester cardiac glycosides in their bodies, rendering them distinctly distasteful to most predators!
Also like monarchs, large milkweed bugs don’t enjoy our chilly winter temperatures, and head south to overwinter in warmer climes. They’ll return as the mercury rises in the spring.
Milkweed bugs do little real damage to milkweeds, so control generally isn’t necessary. Instead, the gardener can simply enjoy observing the vivid colors that signal a vibrant, healthy habitat!
Photo: Masa Nomura
