The Body Parts of a Milkweed Bug

Head

• The head of a milkweed bug is equipped with a proboscis, which works like a straw. The proboscis has two tubes. One tube injects a digestive enzyme into a seed while the other withdraws oils and nutrients. Unlike many other insects, the milkweed bug has both single eyes and compound eyes with antennae positioned between them, on each side. Large and prominent compound eyes have many lenses to provide an acute perception of movement and light changes.

Thorax

• The thorax, located between the head and abdomen, consists of three segments. The pro-thorax is closest to the head and supports two legs, one on each side. The meso-thorax or middle section supports one leg and one outer wing on each side. The section closest to the abdomen is called the meta-thorax. It supports a leg as well as a small, soft wing on each side.

Abdomen

• The abdomen of the milkweed bug contains reproductive organs, the digestive system and the heart. A dorsal vessel acts as a heart by pumping hemolymph through anterior regions of the insect's body. Other systems, such as the respiratory and nervous systems run throughout the insect, from head to abdomen.

Markings

• Characteristic markings found on milkweed bugs are black and orange. Distinctive markings found on the underside of the bug help determine if a milkweed bug is male or female. With both male and female milkweed bugs, the tip of the abdomen is black. The next body segment is solid orange with small black dots at the edge. If the next two segments of the bug each have a black band, it is male. If the bug has two orange segments followed by a black band, it is female. Adult female milkweed bugs tend to be larger than their male counterparts.

Nymphal Stages

• A new milkweed bug, called a nymph, emerges from an egg. At this time it is a miniature version of an adult milkweed bug but with slight difference in body proportions along with underdeveloped wings. As a nymph grows it molts five times. Just after molting, the nymph is creamy yellow in color and has bright red legs. Nymphs grow and more closely resemble an adult milkweed bug with each molt.