Milkweed Bug Information

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Phylum, Arthropoda; Class, Insecta; Order, Hemiptera

Identifying Features

Appearance (Morphology)

  • Milkweed bugs are colored orange (or orange-red) and black.
  • They have a long proboscis which they use to pierce the seed and inject salivary enzymes used to digest their food.
  • Legs are delicate.
  • Adult milkweed bugs have full grown wings which cover the abdomen.

Adult Males and Females
On the underside of the abdomen, the female has one black strip and two black dots. The male has two thick black strips. Adults mate end to end. They may stay attached for 30 minutes or more.

Immatures (different stages)
Milkweed bugs are hemimetabolous insects, i.e. they have incomplete metamorphosis. Therefore the nymphs (immatures) look like the adults except that they do not have full wings and their color pattern is different. Black wing pads appear early in development. Nymphs have bright red abdomens. Milkweed bugs usually molt 5 times (they have 5 nymphal instars before becoming an adult). Eggs take about 1 week to hatch and a month to become adults at room temperature (75°F). Development of milkweed bug is: emergence - (1st instar) - first molt - (2nd instar) - second molt - (3rd instar) - third molt - (4th instar) - 4th molt - (5th instar) - 5th molt (adult).

Natural History

Food
Seeds and tissue of the milkweed plant (Asclepias spp.). In captivity, the bugs feed on shelled sunflower seeds.

Habitat
Milkweed bugs are usually found in small groups on milkweed plants, often on the underside of the leaves. Milkweed plants sometimes fill entire fields in good years, but usually are found along roadways. The plant produces a milky white sap when a leaf is removed. These plants are large (3-4 feet high) with sprays of small white flowers in the summer. In the fall, seed pods develop which are 4 inches long and 1 1/2 inches wide. When the seeds ripen the seed pods open up releasing the seeds which float on fluffy white parasols. Milkweed bugs can be found on seed pods piercing the wall of the pod to feed on seeds.

Predators
Milkweed bugs have few predators because they concentrate in their bodies bad tasting compounds found in the sap of milkweed plants. The bugs use the bright coloration to advertise their bad taste. Inexperienced birds that taste their first milkweed bug are unlikely to try to eat another orange and black insect! Some insects that do not taste bad use similar color patterns to fool birds. These are known as mimics.

Interesting Behaviors
Milkweed bugs often gather in groups on the milkweed plant. This gregarious behavior probably enhances their warning coloration. In the container you may see groups of bugs forming at night. During the day they are usually found feeding on seeds or walking around the container. Sometimes groups form on the side of the container away from the seeds when some of the bugs are molting.

Impact on the Ecosystem

Positive
Milkweed bugs are one of a small group of insects that have the ability to tolerate the toxic compounds in the milkweed plant. They are therefore important in regulating populations of this plant.

Negative
None, unless you are trying to raise milkweed plants!

Collecting Live Insects

Where to find
Milkweed bugs are found on milkweed plants. Look for clusters of brightly colored insects on seed pods, leaves or blossoms. Milkweed bugs can be purchased from: Carolina Biological Supply Company, Connecticut Valley Biological Supply Co., Inc., and Science Kit and Boreal Laboratories.

How to collect
Use old pill bottles or small containers to gather the nymphs and adults. Hold the container below the insect and tap it into the container or use your fingers to gently pluck later instar bugs off the plant. Use an aspirator to gather small nymphs.

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