Many of the pictures and videos on this site are of butterflies and caterpillars. This is mainly because of a garden I built for butterfly larvae (caterpillars).
Most butterflies will eat the nectar and pollen from a number of flowers, but may only lay their eggs on specific types of plants. Monarchs lay their eggs on milkweed, tiger swallowtails lay their eggs on tulip poplars and wild cherry trees, etc... Once hatched, the caterpillars feed on the host plant. In our butterfly garden, fennel and rue attracted black swallowtail butterflies to lay their eggs.
We see about two-hundred caterpillars hatch each year. After feeding for about two weeks, most of them travel somewhere else to form a chrysalis, from which the butterfly will emerge. A few, however, have formed their chrysalis right on the fennel.
If you want to attract and help create more butterflies, take a look at the species you have in your area and find out what plants they need. Pesticides are especially harmful on butterflies, so you'll have to have a safe place to plant your garden. An area protected from wind is helpful, as is an area that gets morning sun. Just be patient. If you plant it they will come.
This T-Shirt of the Eastern Black Swallowtail's lifecycle is available at www.cafepress.com. Click on the image to go to the site where you can buy it.