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What is a Small Milkweed Bug (Lygaeus kalmii)

The Small Milkweed Bug, a vibrant and intriguing insect, plays a unique role in the ecosystems of North America. Adorned with striking red and black markings, this bug is often found in the company of milkweed plants, a testament to its specialized lifestyle.

Small Milkweed Bug (Lygaeus kalmii)

Small Milkweed Bug Overview

While small in size, the Small Milkweed Bug is significant in demonstrating the complex relationships between insects and plants. It’s known for both its beauty and its importance in the life cycle of milkweeds.


  • Kingdom: Animalia (Animal)
  • Phylum: Arthropoda (Invertebrate)
  • Class: Insecta (Insects)
  • Order: Hemiptera (True Bugs, Cicadas, Hoppers, Aphids, and Allies)
  • Suborder: Heteroptera (True Bugs)
  • Family: Lygaeidae (Seed Bugs)
  • Genus: Lygaeus (Seed Bug genus)
  • Species: L. kalmii

There are two recognized subspecies:

  1. Lygaeus kalmii angustomarginatus Parshley, 1919 – eastern small milkweed bug
  2. Lygaeus kalmii kalmii Stal, 1874 – western small milkweed bug
Small Milkweed Bug Lygaeus kalmii (plant bugs)

Size and Body Description

Small Milkweed Bugs are typically about half an inch long. They have a distinctive pattern of red and black on their backs and are recognized by the small, white spots on their wings and the X-shaped marking across their backs.


Approximately 0.5 inches (1.27 cm) in length.


Their primary food source is milkweed seeds, but they also feed on nectar and other parts of the milkweed plant. They are adapted to handle the toxic sap of the milkweed, which provides them with chemical defenses against predators.


These bugs reproduce by laying eggs, typically on or near milkweed plants. The nymphs (juveniles) go through several stages before reaching adulthood. As insects, they play a role in pollination, albeit indirectly, by moving among flowers.


They are widespread across North America, wherever milkweed plants are found.

Where Found

Small Milkweed Bugs are commonly found on or near milkweed plants in fields, meadows, and gardens, where these plants grow.

How Long Do Small Milkweed Bugs Live

Their lifespan, from egg to adult, spans several weeks to months, depending on environmental conditions.


While not endangered, Small Milkweed Bugs depend heavily on the availability of milkweed plants, which are affected by habitat loss and the widespread use of herbicides. Conservation efforts for these bugs are tied to the preservation of milkweed habitats.

The Small Milkweed Bug, with its vivid colors and specialized diet, is a fascinating example of nature’s interconnections. Protecting milkweed habitats not only supports these bugs but also benefits a wide range of other species, including the monarch butterfly.

Small Milkweed Bug (Lygaeus kalmii)