Small vs Large Milkweed Bug: Decoding the Differences

Milkweed plants are home to a variety of insects, two of which are the small and large milkweed bugs. These bugs, although similar in appearance, have some key differences in size and markings. In this article, we’ll explore the characteristics that set them apart and help you identify these fascinating little creatures.

Small milkweed bugs (Lygaeus kalmii) are orange and black with a distinct heart-shaped black patch on their back and two smaller black patches on either side. They grow to a length of about ½ inch and are known to feed on milkweed seeds, as well as nectar from the plants source. On the other hand, large milkweed bugs (Oncopeltus fasciatus) are slightly larger, with a pronounced black band across their middle and diamond-shaped black patches on their backs source.

As you explore milkweed plants, keep an eye out for these colorful insects. Understanding their differences will not only improve your knowledge of the natural world but also help you appreciate the fascinating interactions occurring within this unique ecosystem.

Identifying Milkweed Bugs

Physical Characteristics

Large milkweed bugs (Oncopeltus fasciatus) and small milkweed bugs (Lygaeus kalmii) are part of the true bugs (Hemiptera) family. Both species are characterized by their distinctive orange and black color patterns.

Large milkweed bugs:

• ½ to ¾ inch long
• Orange to reddish-orange with a black band across their back
• Two large diamond-shaped black patches on their wings
• Orange antennae

Small milkweed bugs:

• About ½ inch long
• Reddish-orange X on their back
• Reddish-orange band across the pronotum (shield-like plate between head and wings)
• Black antennae

The Milkweed Bug Life Cycle

Both large and small milkweed bugs undergo complete metamorphosis which includes four stages: egg, nymph, pupa, and adult.

Eggs:

• Light yellow, turning reddish before hatching
• Laid in small clusters on milkweed plants
• Hatch within a week

Nymphs:

• Go through five instars (growth stages)
• Resemble smaller, wingless versions of adults
• Develop wing pads and increased black markings with each molt

Pupa:

• Non-feeding stage before becoming adults

Adults:

• Develop wings for flying and mating
• Feed on milkweed plants, particularly seeds
• Travel south for overwintering (large milkweed bugs)

Habitats and Migration

Small and large milkweed bugs can both be found in North America, particularly in areas where milkweed plants are present. Milkweed is a vital component of their habitat, as both bugs feed on these plants, specifically the seeds. Here are a few notable characteristics of each bug in relation to their habitats and migration patterns:

• Small milkweed bugs are more commonly found in southern Canada, the United States, and parts of Central America¹.
• Large milkweed bugs are primarily found in North America and can be seen throughout the United States and southern parts of Canada².

It is interesting to note that, unlike monarch butterflies, small and large milkweed bugs are not major migratory species¹. Monarch butterflies, on the other hand, undertake an impressive two-way migration from southern Canada to central Mexico each year³.

In some regions, like Illinois, both small and large milkweed bugs can be found as permanent residents¹. Their presence is essential in supporting the ecosystem by helping to control milkweed populations. Additionally, they provide a food source for various predators.

To summarize, small and large milkweed bugs share similarities in habitat preferences and are mostly found in areas rich with milkweed plants. While they do not exhibit the same extensive migratory behavior as monarch butterflies, they still play a significant role in the ecosystem.

Milkweed Bugs and the Milkweed Plant

Seeds and Seed Pods

Milkweed plants produce seeds that are enclosed in seed pods. These pods open in the fall and release seeds with silky hairs allowing them to be carried away by the wind. You can often find two types of milkweed bugs, the large milkweed bugs (Oncopeltus fasciatus) and small milkweed bugs, on the seed pods. They both feed on milkweed plant parts, especially the seeds.

For example, large milkweed bugs are ¾” long and have a reddish-orange color with a black band across their back. Both adults and nymphs can be found clustering on the seed pods.

Milkweed Plant Selection

There are many different species of milkweed plants, such as common milkweed (Asclepias syriaca), swamp milkweed (Asclepias incarnata), and butterflyweed (Asclepias tuberosa). They all share characteristics like leaves, stems, flowers, and roots, but they may vary in size, shape, and color.

When selecting milkweed plants for your garden, you can consider their features and choose the ones that best suit your preferences. Here are some of their characteristics:

• Common milkweed (Asclepias syriaca):
  • Broad leaves
  • Pink flowers
  • Tolerant of various soil types
• Swamp milkweed (Asclepias incarnata):
  • Narrow leaves
  • Light pink to mauve flowers
  • Prefers wet soils
• Butterflyweed (Asclepias tuberosa):
  • Narrow leaves
  • Orange flowers
  • Prefers well-drained soils

In addition to the above species, you can also find other varieties like whorled milkweed (Asclepias verticillata), and even giant milkweed (Calotropis gigantea), which can grow up to 15′ tall and 15′ wide. By choosing the right milkweed plants for your garden, you can provide a habitat for milkweed bugs, monarch butterflies, and other pollinators.

The Role of Milkweed Bugs in the Ecosystem

Milkweed bugs, including both large and small varieties, play a significant part in the ecosystem. They mainly feed on milkweed plants and are often associated with monarch butterflies.

Large Milkweed Bug

The adult large milkweed bug (Oncopeltus fasciatus) is ¾” long, orange to reddish-orange, with a black band across its back. They are most commonly found clustering on seed pods of milkweed plants.

Small Milkweed Bug

The small milkweed bug (Lygaeus kalmii) grows up to ½ inch long, has a black color with a large red X-shape on its back, white margins on its wings, and a red band on its pronotum.

Insects that rely on milkweed:

• Monarch caterpillars
• Milkweed tussock moth
• Longhorn beetle
• Swamp milkweed leaf beetle

Milkweed bugs are part of a larger group of insects that rely on milkweed plants. Each of these insects has a unique relationship with milkweed. For example, monarch caterpillars feed exclusively on milkweed, as its toxic compounds called cardiac glycosides help protect them from predators. However, large and small milkweed bugs don’t consume the entire plant; they focus mainly on seeds.

Similarly, other bugs like the milkweed tussock moth caterpillar (Euchaetes egle) and the longhorn beetle (Tetraopes tetrophthalmus) also rely on milkweed plants for their survival.

Comparison of milkweed insects:

While milkweed bugs may seem like they only have a small role in the ecosystem, you must remember that they are closely connected to a larger group of insects that all rely on milkweed plants. This dependency creates a complex web of interactions essential for a diverse and thriving ecosystem. By understanding the importance of these bugs and their role in the environment, you can appreciate the value of preserving milkweed plants and supporting the overall ecosystem.

Reproduction and Predation

When it comes to reproduction, both small and large milkweed bugs have unique strategies to ensure the survival of their species. Let’s explore their reproductive behaviors and their interactions with predators.

Small milkweed bugs (Lygaeus kalmii) and large milkweed bugs (Oncopeltus fasciatus) are known to make their home on milkweed plants, where they feed on plant seeds and living tissue. During the breeding season, males and females engage in mating behaviors that involve the transfer of pair-forming pheromones.

In contrast, aphids like Aphis nerii or the oleander aphid have a different reproductive strategy. They are able to reproduce both sexually and asexually through a process called parthenogenesis. This allows them to produce offspring without the need for male fertilization. For most parts of the year, females reproduce asexually, giving birth to live young. However, when environmental conditions change, they switch to sexual reproduction, which leads to the production of male and female offspring.

Predators such as ladybird beetles and lacewing larvae feed on both milkweed bugs and aphids. These predators help maintain a balance in the ecosystem by limiting the population of these herbivores. Common predators to milkweed bugs include insects like assassin bugs and ants, as well as mammals like birds and rodents. Predation is a natural part of the ecological balance and ensures that milkweed bug and aphid populations do not grow out of control, causing potential harm to their host plants.

In conclusion, milkweed bugs and oleander aphids showcase distinct reproductive strategies that ensure their survival in their respective habitats. Although they share some predators, their individual reproductive behaviors differentiate them in how they respond to these challenges.

Interactions with Other Organisms

The Effect on Monarchs

Milkweed plays a crucial role as a host plant for the monarch butterfly. When caterpillars feed on milkweed, they ingest the plant’s toxic latex, which offers them protection against predators. However, milkweed beetles may damage the buds and hinder the growth of new leaves on the milkweed, leading to stunted and deformed plants. This could negatively affect monarch butterflies by reducing the available food and habitat for their caterpillars.

With regards to milkweed tussock moth caterpillars, they eat milkweed leaves and may consume entire plants, with the exception of major veins which contain the latex sap. Unfortunately, this can potentially limit the resources for monarch caterpillars, as the leaf consumption is sometimes especially noticeable.

Interactions with Other Insects

Milkweed plants are also attractive to various other insects, such as honeydew-producing aphids. Honeydew is a sugary liquid secreted by these aphids that can cover the milkweed leaves, providing a food source for sooty mold which can stunt plants’ growth. On a positive note, aphids’ presence can attract beneficial insects like lacewings that help control aphid populations. To preserve the beneficial insects, it is recommended to avoid using insecticides on milkweed plants.

Milkweed tussock moth caterpillars, with their dense hair (tufts), make a striking appearance compared to the hairless monarch caterpillars. After maturing, they spin a gray cocoon and pupate. Although these caterpillars are predominantly native to the eastern United States, they’ve also been reported in the Mediterranean region.

Potential Threats and Solutions

Both the small milkweed bug and the large milkweed bug feed on milkweed plants. However, their feeding habits can present challenges for milkweed and the insects that depend on them.

Toxic Compounds

Milkweed plants contain toxic compounds called cardenolides. These toxins are a defense mechanism against potential predators. Fortunately, milkweed bugs have evolved to tolerate these toxins. As they feed on milkweed, they not only consume these toxic compounds but also store them in their bodies. This strategy makes them unappetizing and potentially harmful to their predators.

Saliva

Milkweed bugs have specialized piercing-sucking mouthparts that allow them to feed on plant sap, seeds, and leaves. As they pierce the plant tissue and inject their saliva, they can cause damage to the plant, affecting its overall health and growth. Moreover, their saliva can facilitate the spread of potential diseases, leading to further threats to the milkweed plant.

Solutions

To protect milkweed plants and their dependent insect populations, consider the following:

• Plant native milkweed species in your area to strengthen their resistance to potential threats.
• Monitor milkweed plants for the presence of milkweed bugs and other pests and manage them accordingly.
• Maintain a diverse garden by including various plants to support different insects and provide natural predators to control pests.

By following these steps, you can create a thriving environment that supports milkweed plants and the insects that depend on them, like the monarch butterfly, without being overrun by milkweed bugs.