Butterflies undergo a transformation throughout their lives, a process known as complete metamorphosis. This biological journey involves distinct stages, where the insect changes its form and activities dramatically. Unlike animals that simply grow larger, butterflies experience a remarkable reshaping of their bodies, evolving through several different appearances. These changes allow them to fulfill different roles at each phase of their existence.
From Tiny Egg to Growing Caterpillar
A female butterfly lays her eggs, often on specific host plants. Each butterfly species has preferred host plants, such as milkweed for Monarchs or plants from the parsley family for Black Swallowtails, which provide food for the caterpillars. These eggs, which can be round, oval, or cylindrical depending on the species, are typically laid in clusters and can vary in size, though many are quite small. After a few days to a few weeks, a larva, commonly known as a caterpillar, hatches from the egg.
The primary function of the caterpillar is to eat and grow rapidly. Its diet consists almost exclusively of the host plant leaves it was born upon, consuming them voraciously to fuel its development. As the caterpillar grows, its rigid outer skin, or exoskeleton, does not expand, necessitating a process called molting. During a molt, the caterpillar sheds its old skin, revealing a new, larger one underneath. Most butterfly caterpillars undergo four to five molts, with the stages between molts referred to as instars, increasing their size significantly.
The Remarkable Chrysalis Stage
Once the caterpillar has reached its full size, it prepares for the next stage by finding a secure spot. It typically attaches itself to a surface, such as a twig or leaf, using a silk pad and its hind legs, often hanging upside down in a “J” shape. The caterpillar then undergoes one final molt to reveal the pupa, which in butterflies is specifically called a chrysalis.
The chrysalis is a hardened outer casing that protects the transforming insect within. It differs from a moth’s cocoon, which is a silken structure spun by the moth larva around itself for protection. Inside the chrysalis, cellular reorganization occurs; most of the caterpillar’s body tissues break down into a liquid mass, while specialized cells, known as imaginal discs, form the structures of the adult butterfly. The duration of this stage varies from a few weeks to several months or even a year, depending on the butterfly species and environmental factors like temperature.
Emerging as a Beautiful Butterfly
As the butterfly prepares to emerge, the chrysalis often becomes transparent, revealing the adult butterfly’s wing patterns and colors. The butterfly then pushes, causing the chrysalis to split, allowing it to break free. The emerged butterfly has soft, damp, and crumpled wings.
To expand its wings, the butterfly pumps hemolymph from its abdomen into the wing veins. This hydraulic pressure unfurls and stretches the wings to full size. After expansion, the butterfly must rest while its wings dry and harden, preparing for flight. The adult butterfly’s primary purpose is to reproduce and it often feeds on nectar.