Their characteristic orange and black carapace may give milkweed bugs an intimidating appearance, but they don't bite, sting or pose a threat to people. Gardeners growing milkweed plants may consider these bugs pests, though, since they vigorously consume the seeds and sap of the plant they are named after.
Small and Large Milkweed Bugs
Identifying a milkweed bug is actually a bit confusing, because the term describes two different insect species. The large milkweed bug (Oncopeltus fasciatus) and small milkweed bug (Lygaeus kalmii) have similar life cycles, appearance and diet. Both species consume the seeds of milkweed plants for sustenance and reach maturity without a distinct metamorphic phase, like butterflies and moths do. Small and large milkweed bugs are both members of the taxonomic order Hemiptera, which contains the insect species known as "true bugs," according to FOSS Web.
Adult milkweed bugs lay eggs in narrow, protected cavities around the pods of milkweed plants. A single female lays several dozen eggs a day on average, which can result in a total of up to 2,000 eggs over a 30-day lifespan, according to My Monarch Guide. Females deposit their orange or yellow eggs in clusters. It takes 4 to 10 days for the eggs to hatch, with an average hatch time of one week. Warmer weather reduces the amount of time needed for the eggs to hatch. An adult male may fertilize a female bug for up 30 minutes before she deposits eggs.
The immature milkweed bug that emerges from the egg is called a nymph. The bugs don't go through a larval stage, so the nymphs bear a close physical resemblance to their adult parents. They aren't exactly alike though. Nymph bodies have a different color pattern and are much smaller than adults. They also lack wing pad structures on their back until they mature, according to University of Arizona Center for Insect Science. Milkweed bug nymphs develop through five distinct stages, or "instars," which are marked by a brief molting phase. The nymph becomes a fully mature adult after the fifth molting phase.
Milkweed bug adults are relatively safe from predators in the wild, because they spend most of their time huddled within the seed pod of their host plant. They suck out the sap from the seeds, which can damage the plant over time. Their primary source of food also affords them a natural defense. Milkweed sap contains cardiac glycosides and other toxic chemicals, according to My Monarch Guide. Milkweed bugs aren't affected by the chemicals, but they retain the toxins inside their bodies to discourage predatory birds and animals.
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