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Bug of the Month: Small milkweed bug

brown lipped snailCommon name: Small milkweed bug

Latin name: Lygaeus kalmii

Kingdom Animalia
   Phylum Arthropoda
      Class Insecta
         Order Hemiptera
            Family Lygaeidae


Seed bugs in general

Seed bugs (Family Lygaeidae) are “true bugs” in the order Hemiptera. All species within the Hemiptera (literally, “half wing”) have forewings which are hardened in the front and membranous in the back. Another distinctive feature of true bugs are their long, segmented, straw-like mouthparts or “beak.” The beak consists of two parallel tubes, one for sending saliva into the food to help digest it and the other for sucking up the mix of saliva and food. While some species of true bugs are predators and use their beak to eat other insects, most seed bugs use their beaks to pierce and feed on seeds.

Seed bugs are hemimetabolous; they do not go through a complete metamorphosis as they mature. As in other arthropods that are hemimetabolous, the immature seed bugs (or nymphs) resemble the adults, without developed wings or functional genitals. The nymphs go through a number of stages, called instars, before reaching their adult stage. Between each instar, they shed their old skins to grow larger in size.

The family Lygaeidae has been “reorganized” in recent years, with many of the former subfamilies of seed bugs now placed in their own families. For example, chinch bugs, which can be major crop and lawn pests, are now in the family Blissidae. The remaining Lygaeids include the large and small milkweed bugs.

How to identify small milkweed bugs

Small milkweed bugs, Lygaus kalmii, are usually 10 to 12 millimeters long and are black with orange bands on the forewings that form an “X.” Their heads are also black with a red spot on the top which often extends to the face. The black pronotum has a broad red band. As their name suggests, these insects are associated with milkweed plants. However, there are many red and black insects found on milkweed, including the large milkweed bug (Oncopeltus fasciatus), so look carefully at the color pattern.

Where to find small milkweed bugs on the Boston Harbor Islands

Lygaeus kalmii are usually found on milkweed plants, either in clusters or individually. Milkweed is present on many of the harbor islands, usually in meadows and open areas.

How small milkweed bugs make a living

Small milkweed bugs are one of a number of insect species that make their living on milkweed.  Other species include monarch butterflies, large milkweed bugs, and milkweed beetles. Interestingly, all of these insects share a basic color pattern of black and red/orange. These bright patterns are to warn predators that the insect tastes bad! Milkweed plants contain toxins that the insects take into their bodies when feeding. The insects are not harmed by the toxins, but predators don’t like the taste of the insects, so after tasting a black and orange insect, they learn to leave them alone!

Although the small milkweed bug’s name might suggest that these insects survive on milkweed alone, they can survive on other sources of food as well. Adults mainly feed on milkweed seeds, but they often consume nectar from various flowers. They may even be predators or scavengers in times when milkweeds and flowers are not available.

Small milkweed bugs lay their eggs in the spring on milkweed plants, and the eggs hatch into nymphs. These nymphs resemble the adult insects more and more as they develop through several instars to become mature adults. Once winter approaches, the adults are able to overwinter.

Where in the world small milkweed bugs occur

Small milkweed bugs live in most of North America, from southern Canada down through Mexico. They are usually found in places where the climate is suitable for milkweed plants. 

To learn more about small milkweed bugs (and true bugs in general)

On the web:

In print:

    Slater, J.A. and R.M. Baransowski. 1978. How to know the true bugs (Hemiptera-Heteroptera). W.C. Brown Co. Dubuque, IA.