Monarch butterflies undergo a complex transformation, moving through distinct life stages from egg to adult. This process, known as complete metamorphosis, involves a pupal stage where the caterpillar reorganizes its body. Many people mistakenly refer to this stage as forming a “cocoon,” but monarch butterflies, like all butterflies, form a chrysalis.
From Caterpillar to Chrysalis: The Prep Stage
Monarch caterpillars prepare for their transformation during their final, fifth instar. A key behavioral change occurs when the caterpillar stops feeding and begins to wander away from its milkweed host plant, searching for a secure location to pupate. This wandering ensures the vulnerable chrysalis is hidden from predators.
Upon finding a suitable spot, often on the underside of a leaf or stem, the caterpillar spins a small silk pad. It then attaches its rear prolegs to this silk pad and hangs upside down in a distinctive “J” shape. This “J” phase can last from 8 to 36 hours, depending on temperature. During this time, the caterpillar’s tentacles may become limp and twisted.
It is important to note that monarch butterflies do not spin cocoons. Cocoons are silken coverings spun by most moth caterpillars to protect their pupa. In contrast, butterflies form a chrysalis, which is the hardened skin of the caterpillar itself, without any silk covering.
Chrysalis Formation and Appearance
The actual formation of the chrysalis is a rapid and intricate process. After hanging in the “J” shape, the caterpillar begins to shed its skin for the final time. The old skin splits behind the head and peels back, revealing the new, soft chrysalis underneath. The chrysalis then undergoes a series of wiggling movements to fully shed the old skin, which often remains bunched at the top near the silk pad.
Initially, the newly formed chrysalis is soft and may appear bumpy, with a pale greenish-yellow color. Within a few hours, it hardens and takes on its characteristic smooth, jade-green appearance. A monarch chrysalis is typically about 2.5 cm (0.98 inches) long and 10–12 mm (0.39–0.47 inches) wide, though size can vary. It is adorned with a distinctive band of metallic gold spots near the top, which some sources describe as resembling a “golden collar.” These markings help camouflage the chrysalis in its natural environment.
The Chrysalis Stage: Duration and Transformation
The chrysalis stage represents a period of profound internal reorganization, known as metamorphosis. This stage typically lasts between 8 to 15 days under normal summer temperatures. Environmental factors, particularly temperature, significantly influence this duration; warmer conditions can shorten the period, while cooler conditions can extend it.
Inside the seemingly dormant chrysalis, the caterpillar’s body undergoes a complete transformation. Most of the caterpillar’s tissues break down into a nutrient-rich fluid, and specialized cells, called imaginal discs, rapidly develop into the adult butterfly’s structures, including wings, legs, and antennae. This biological process completely rebuilds the insect’s internal systems.
As the butterfly nears emergence, the chrysalis undergoes visible changes. Approximately 24 to 48 hours before the adult butterfly emerges, the chrysalis darkens and becomes transparent. This transparency allows the black, orange, and white wing patterns of the developing butterfly to become visible through the chrysalis casing. The chrysalis does not truly become transparent; rather, the pigment in the butterfly’s wings develops, making the colors visible from the outside. A small opening or unfolding may appear near the top of the chrysalis, signaling that emergence is imminent, often within 90 minutes.