A side advantage of fennel is that it attracts Black Swallowtail butterflies like this one.
The butterflies lay eggs on the fennel and caterpillars, like this one, hatch. They chow down on the leaves, stems and flowers, but do very little damage to the plant.
I've seen the chrysalises produced by these caterpillars, but have never caught a butterfly emerging from one of these. So, a couple of weeks ago, when I found one of these I put it in a jar where I could watch it every day and hopefully see the butterfly emerge.
It is difficult to believe a butterfly could come from such a strange object! Anyway, I put this in a jar and put it on our front porch.
About a week later, I noticed the chrysalis began to darken.
The next day it looked like this. You can actually see the wings of the butterfly inside.