Of the 18,500 butterfly species worldwide, every species relies on a host plant to provide food for its larvae. Fennel is one of the host larval plants for the anise swallowtail butterfly, a common butterfly found along the western coast of North America.
Here in northern California we have a lot of wild fennel–found along freeways, in parks and yards, city parking lots and pavement cracks. This is great news for the anise swallowtail butterfly who depends on fennel to begin life. It’s great news for us, too; our summers are consistently decorated with this large butterfly.
The host larval plant provides the food vitally necessary for the young caterpillar stages, or instars, of the butterfly. When they form wings and fly off, they seek primarily nectar thereafter, because they no longer have mouthparts for chewing.
Observing a butterfly’s four-stage life cycle is fascinating. Most of us know the general story: eggs, larva (caterpillar), pupa (chrysalis), butterfly. We often share this miracle with the children in our lives. Butterfly – Wikipedia.
Athena and I have watched the many stages of this butterfly in the fennel patch in our yard, brought guests young and old to see, too. Then one day last month we were elsewhere, on a trail overlooking the Pacific Ocean, when Athena spotted an adult female butterfly behaving oddly.
The adult was on fennel, for one thing, and not drinking nectar from a flower.
She took a few photos and in examining them later, discovered that the butterfly had deposited an egg on the fennel. (This species lays eggs singly.)
Here you can see the swallowtail’s curved rear end touching down on the fennel. The egg is microscopic, so you won’t see it here.
They start out as a tiny dot on the underside of a plant leaf. All alone it grows from an egg into several successive caterpillars; then forms an exclusive protective shelter around itself as it changes life forms yet again. Eventually it emerges with wings, waits for them to dry, and then flies away. Quite a remarkable feat.
Last weekend we went down to our fennel patch to see if there was any Lepidoptera activity.
We found this one caterpillar, below. It is about the length of a staple. It is one of the first caterpillar instars. Two or three more times the ever-transforming being will eat voraciously until it splits its skin. A new skin will have formed underneath, and the caterpillar will crawl off in it.
One day the adult will flutter by in all its majestic beauty.
Written by Jet Eliot.
All photos by Athena Alexander.