The milkweed plant (Asclepias spp.) is widely known as the sole host for the Monarch butterfly (Danaus plexippus) to lay its eggs. While the Monarch’s pale, ridged eggs are often the primary focus of inspection, milkweed is a complex ecosystem that attracts many other specialized insects. Identifying the eggs of these other species is important for conservationists and gardeners, as it allows them to distinguish between the Monarch’s offspring and other insects that also rely on the plant for their life cycle.
True Bugs: The Seed and Stem Feeders
Several species from the order Hemiptera, commonly known as true bugs, also use milkweed for reproduction and feeding. The Large Milkweed Bug (Oncopeltus fasciatus) and the Small Milkweed Bug (Lygaeus kalmii) are the two most frequently observed species. These insects possess piercing-sucking mouthparts, which they use to feed primarily on the developing seeds within the milkweed pods, impacting the plant’s seed production.
Female Large Milkweed Bugs lay their eggs in small clusters, often hiding them in the crevices of seed pods or other protected areas on the plant. The eggs are initially light yellow, but they quickly turn a reddish or bright orange color before hatching. The Small Milkweed Bug has a similar life cycle and egg-laying habit, laying a brood of up to 15 oval, bright orange-red eggs. Because these true bugs feed on the seeds, they generally do not threaten the Monarch’s food source (leaf tissue).
Beetles and Weevils: Leaf and Root Predators
Milkweed also hosts several species of beetles (Coleoptera), which have distinct egg-laying and feeding patterns. The Milkweed Leaf Beetle (Labidomera clivicollis) lays its eggs on the underside of milkweed leaves. These eggs are deposited in clusters and may be orange or jellybean-like in appearance. Upon hatching, the larvae are pudgy and orange or gray, immediately beginning to graze voraciously on the leaves.
The Milkweed Stem Weevil (Rhyssomatus lineaticollis) focuses its reproductive efforts on the plant’s structural integrity. The female weevil chews a series of holes into the lower part of the stem, laying a single egg inside each one. The resulting larvae tunnel through and feed on the stem’s central pith tissue, which can weaken the plant significantly. This internal damage can cause the upper stem and leaves to wilt and break off, reducing the foliage available for Monarch caterpillars.
Other Lepidoptera: The Milkweed Tussock Moth
The Milkweed Tussock Moth (Euchaetes egle) is another common Lepidopteran that uses milkweed as a host plant. The female moth deposits her eggs in masses, typically on the underside of a milkweed leaf. These egg masses are pale gray, off-white, or fuzzy in appearance, containing dozens of eggs in a tight cluster.
The Tussock Moth larvae hatch from these clusters and initially feed together in large, gregarious groups. Their early feeding behavior involves skeletonizing the leaves, consuming the tissue between the veins while leaving the larger veins intact. This group feeding is a distinct contrast to the solitary nature of the Monarch caterpillar.
Identifying Eggs and Managing Competition
Differentiating a Monarch egg from the eggs of other milkweed specialists is primarily a matter of close inspection. A Monarch egg is tiny, ovoid, pale yellow or creamy white, laid singly, and features distinct vertical ridges.
Egg Identification
- The Milkweed Tussock Moth lays fuzzy, off-white clusters without the Monarch’s characteristic ridges.
- The Large Milkweed Bug eggs are found in small, reddish-orange clusters, often hidden in seed pods, and lack the conical shape of the Monarch egg.
- The Milkweed Stem Weevil eggs are nearly invisible, being deposited inside the plant’s stem tissue.
For gardeners concerned about competition, manual removal is the most effective management strategy. Insects like the Milkweed Leaf Beetle and the Milkweed Bugs can be hand-picked or flicked into a bucket of soapy water. Tussock Moth egg masses can be removed entirely by pinching off the small section of the leaf where they are clustered. Careful inspection is paramount; a gardener must ensure they are not accidentally removing a Monarch egg or small caterpillar, which can be protected by relocating them to an uninfected plant.