Just like the list for nectar plants, there are numerous host plants that serve as food for caterpillars. Depending upon your region and plant zones, there are regionally specific butterflies that occur there. A visit to your local extension service or native plant nursery might answer the questions of which butterflies occur in your neighborhood and what plants to include for them.
Some caterpillars are generalists, others more specific in their selection. One example of this is the monarch and the milkweed relationship. Monarch butterflies lay their eggs mostly on milkweeds.
As the young feed on the leaves, they develop toxicity from consuming glycosides in the leaves. This and their coloration deter most predators; of course, when a jay eats the caterpillar it gets ill.
In my yard I plant a mix of host plants with flowering plants in the hopes that adult butterflies and moths will select these plants on which to lay their eggs. This list includes dill, parsley, cow parsnip, cabbage, mint, willow, aspen, sunflowers, milkweeds, sunflowers and hollyhocks. I am willing to sacrifice some plants to the appetites of the caterpillars in exchange for beautiful butterflies.
I also try to stay vigilant and watch for excessive numbers of caterpillars. A few of these I transfer to a terrarium and keep them supplied with host plant vegetation. With a wire mesh top, I can keep these caterpillars in captivity and then photograph them in their different life stages of chrysalis and adult.
I have also taken advantage of neighbors whose trees overhang our fences and whose limbs bear caterpillars. I might snip off a few branches and put these in the terrarium. Of course, I'm denying some birds of food, but the temptation to "grow" some butterflies is too much.
The other caterpillars that I let live are the tomato hornworms. These beastly looking caterpillars can do a lot of damage on tomato plants, but again this is a trade-off. I may lose some tomato leaves, but these horned (on the rear end) caterpillars will eventually burrow into the soil and pupate. The caterpillars will morph into a magnificent sphinx moth or hawk moth. The large adults are often confused with hummingbirds when they hover in front of flowers seeking nectar.
If I need more incentive to provide host plants, I check out the National Pollinator Week's website at www.pollinator.org. It doesn't take much visiting to understand the importance of pollinators to crops, orchards and gardens. Certainly some of the plants that I've included for the caterpillars are used by other pollinators gathering nectar or pollen. Some of the butterflies and moths that have fed on my plants as caterpillars may also play the pollinator role as adults. My big picture vision helps me incur the in-the-moment damage by the caterpillars; I know I'm contributing to the greater good by planting host plants.