Experienced butterfly gardeners know their gardens need both nectar plants, for adult butterflies, and host plants, for caterpillars to eat. The best butterfly gardens provide places for every part of the butterfly life cycle, from egg to caterpillar, chrysalis to adults. This series of posts explores each of these butterfly life cycle steps, and how your own garden can better support butterflies during those steps.
After several weeks of eating non-stop, a caterpillar finally reaches full size. Now it’s ready for the big transformation into an adult butterfly. This takes time, too. The caterpillar often begins by crawling away from the host plant it’s been feeding on, looking for a safe, hidden place. (This is why it often seems like the caterpillars in your garden “disappear” without becoming b butterflies – they may have crawled up to 100 yards away!)
Once there, the caterpillar uses its spinnerets, located next to the mouth, to create a tiny silken pad. The caterpillar then carefully attaches itself to the pad using a hook at its rear end, called a cremaster. The it drops to hang in a “J” shape. Some caterpillars, like sulphurs and swallowtails, also spin a single thread around their middle as a kind of sling for extra support.
Now the caterpillars prepares for its final molt. It purges any excess food waste from its gut, and seems to shrink and dry out. The body feels tight if you touch it at this point. Tubercles lose their stiffness and look withered. After a day or two, the caterpillar’s body begins to twitch. The skin at the head splits open, and the caterpillar begins wiggling out of it, still hanging upside-down. Eventually, the skin falls to the ground, leaving only the soft chrysalis (also called a pupa) beneath. Over several hours, the skin of the chrysalis hardens to provide a bit more protection.
The chrysalis (not a cocoon – learn more here) can take a variety of forms. Each species of butterfly has evolved a chrysalis shape that best blends into its environment. A Giant Swallowtail looks almost exactly like a twig on a branch. Many others look like leaves, green or brown. Some are firm and motionless; others have the ability to twitch to scare off predators. Often, they look like they have flecks of gold, though this is just a trick of the light. It’s those gold flecks that give the chrysalis (pronounced KRISS-uh-liss) its name, from the Greek for gold.
While the chrysalis hangs motionless for about two weeks (longer in species that overwinter in chrysalis), the transformation inside is nothing short of amazing. Without getting overly technical (click here if you’d like a detailed description), it’s fair to say that the caterpillar’s body self-destructs, cell by cell. Each cell has a specific purpose in the developing butterfly’s body, and the enzymes that destroy the cells are also activating their new purpose. Wing cells, which have lain dormant all this time, now awake and begin to take shape. As the days progress, the process speeds up, until the butterfly inside is fully formed. (See amazing 3-D scans of butterfly development inside the chrysalis here.)
At the very end, the chrysalis changes too. The skin thins, showing more of the butterfly inside. At last, that skin cracks open, and the adult butterfly begins to emerge. The final stage of the butterfly life cycle is about to begin.