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A Nature Journal

Experience the natural world with east central Illinois master naturalists
Milkweed Bug Pic

Another Colorful Creature Found on Milkweeds

Posted by Bethany Semancik -

With all the talk about milkweeds, some of you may have planted a few to create habitat for the benefit of the Monarch Butterfly. (It's the one year anniversary of an article on Illinois milkweeds and Monarchs which appeared in the December, 2014 Field Notes.) As a dividend, you may have attracted some really beautiful little creatures called milkweed bugs. They are in the order Hemiptera, otherwise known as "true bugs." Rather than having mouths used for biting and chewing food, true bugs have a tube for sucking fluids.

The handsome Large Milkweed Bug, Oncopeltus fasciatus, featured in this article, is about 0.7 inches long and is shown feasting on the flowers of a Swamp Milkweed plant, generally sucking nutrients from the milkweed seeds. This insect species has a big yellow, orange, or red "X" on the back of the forewings with a black band or bowtie going through the middle. The bugs go through a simple metamorphosis, emerging from the egg looking like a very small adult with incompletely developed wings. Instead of wings, they have black wing pads. As the larvae eat, they grow in size and usually molt five times (instars) on their path to adulthood.

It all begins with a male and female mating. The female lays small, bright red, elongated eggs in spring (30/day and over 1,000 in a life span) in or between the milkweed pods. These eggs hatch in about a week and the larvae become adults in about a month. This allows for more than one generation per year.

While the larvae are growing their wings, they appear mostly orange in color with some black spots on the posterior side of the abdomen.

The milkweed sap is toxic, and the Milkweed Bugs concentrate the toxic chemicals in their bodies. They advertise their bad taste with their bright colors, and, as a result, they have few predators. The adults are quite abundant until the first frost when they migrate south. Then they seek out a place in plant or wood debris to overwinter as they hibernate.

Milkweed bugs are widely distributed throughout the United States, but they are rare in the southeast and in the Rocky Mountains. They're generally found in fields and meadows where there are milkweeds.

In addition to the Large Milkweed Bug, there is a Small Eastern Milkweed Bug, Lygaeus kalmii, which is about half the length, and black, red, and quite colorful. All of these bugs do little damage, but they can be controlled with insecticidal soaps or chemical insecticides. Meanwhile, enjoy their color and company.

Story and Photo by Dick Robrock (2007)

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