Food Plants that provide Larval Food
(feed caterpillars) for Butterflies
Unless you are plagued with them, let some of the caterpillars in your garden pupate so that they can emerge as beautiful butterflies. The smaller the caterpillar, the less damage it will do to your plant / garden. In a corner of your garden, plant some plants that the larva/caterpillars can feed on (host plants). Butterflies often lay their eggs on these plants so that when the caterpillar emerges, it has a ready food supply. These plants include a few garden flowers, some trees, vegetables, weeds, and wildflowers.

Here's a list of host plants that provide a larval food source / feed caterpillars:
Alder: Alders are a good food source for caterpillars of the Western Tiger Swallowtail Butterfly.
Alfalfa: Alfalfa is a favorite food source for the caterpillars of butterfly species including the Orange Sulphur, the Marine Blue, the Ceraunus Blue, the Southern Dogface, and the Funereal Duskywing.
Agaves: Agaves provide food for the caterpillar of the California Giant-Skipper Butterfly.
Bladderpod: Bladderpods feed the caterpillars of the Becker's White Butterfly.
Broccoli: Broccoli feeds the caterpillars of the Cabbage White Butterfly.
Buckwheat: The different varieties of Buckwheat are a favorite food source for the caterpillars of a number of butterfly species including the Bright Blue Copper, the Gorgon Copper, the Bramble Hairstreak, the Gray Hairstreak, the Square-Spotted Blue, the El Segundo Blue, the Acmon Blue, the Lupine Blue, the Veined Blue, the Painted Lady, and the Mormon Metalmark.
Burdock: Burdock feeds the caterpillars of the Painted Lady Butterfly.
Cabbage: Cabbage is a great food source for the caterpillars of the Cabbage White Butterfly.
Carrot: Carrot leaves are a good food source for caterpillars of the Black Swallowtail Butterfly and the Anise Swallowtail Butterfly. 
Cassia (Senna): Cassias are a great source of food for the caterpillars of the Cloudless Sulphur Butterfly and the Sleepy Orange Butterfly.
Celery: Celery leaves feed the caterpillars of the Black Swallowtail Butterfly.
Chuparosa: Chuparosa is a food plant for the caterpillar of the Tiny Checkerspot Butterfly.
Citrus: Various types of citrus trees feed the caterpillars of the beautiful Giant Swallowtail Butterfly and the 'Desert' Black Swallowtail.
Cottonwood: Cottonwoods offer a good food source for the caterpillars of the Western Tiger Swallowtail Butterfly, the Mourning Cloak Butterfly, and the Weidemeyer's Admiral Butterfly.
Dutchman's-Pipe: Dutchman's-Pipe feeds the caterpillar of the Pipevine Swallowtail Butterfly.
Elm: Elms provide food for the caterpillars of the Mourning Cloak Butterfly.
False Indigo: False Indigo feeds the caterpillars of the California Dog Face Butterfly.
Grasses: All kinds of grasses feed a variety of caterpillars of a number of butterfly species including the Orange Skipperling, the Common Branded Skipper, the Fiery Skipper, the Sandhill Skipper, the Eufala Skipper, the Woodland Skipper, the Rural Skipper, the Umber Skipper, the Riding's Satyr, possibly the Canyonland Satyr, the California Ringlet, and the Great Basin Wood-Nymph.
Hackberry: Hackberries provide food for the caterpillars of the American Snout Butterfly and the Hackberry Emperor Butterfly.
Paintbrush: The different varieties of Paintbrushes including the Indian Paintbrush, provide food for the caterpillars of the Leanira Checkerspot Butterfly, Variable Checkerspot Butterfly, and Edith's Checkerspot Butterfly.
Junipers: A variety of junipers feed the caterpillars of hairstreak Butterflies including the 'Siva' Juniper Hairstreak, the 'Loki' Juniper Hairstreak, and the Juniper Hairstreak.
Lupine: Different kinds of lupine feed the caterpillars of the Arrowhead Blue Butterfly, the Melissa Blue Butterfly, the Boisduval's Blue Butterfly, the Gray Hairstreak Butterfly, and the Silvery Blue Butterfly.
Mallow: A variety of mallows make a good food source for the caterpillars of a number of butterfly species including the Gray Hairstreak, the West Coast Lady, the Common Checkered-Skipper, the White Checkered-Skipper, the Northern White-Skipper, and the Painted Lady.
Marigold: Marigolds feed the caterpillars of the Dainty Sulphur Butterfly.
Mesquite: Varieties of Mesquite feed the caterpillars of the Ceraunus Blue Butterfly, the Palmer's Metalmark Butterfly
Milkweed: Milkweed is a favorite food source for the caterpillars of the Monarch Butterfly and the Queen Butterfly.
Mistletoe: Growing on cottonwoods, live oaks, sycamores, junipers and pine - Mistletoe provides food for the caterpillars of the Great Purple Hairstreak Butterfly.
Monkeyflower: Different Monkeyflowers provide food for the caterpillars of the Common Buckeye Butterfly and the Variable Checkerspot Butterfly.
Mustard: Mustard is an excellent food source for the caterpillars of the Checkered White Butterfly, the Cabbage White Butterfly, and the Sara Orangetip Butterfly.
Nettle: A variety of nettles - including stinging nettle - feed the caterpillars of the Red Admiral Butterfly, the West Coast Lady Butterfly, Milbert's Tortoiseshel Butterfly, the Satyr Comma Butterfly, and the Painted Lady Butterfly.
Oaks: A variety of Oaks and Live Oaks offer a good source of food for the caterpillars of a number of butterfly species including the Great Purple Hairstreak, the Golden Hairstreak, the California Hairstreak, the California Sister, the Propertius Duskywing, the Mournful Duskywing, and the Colorado Hairstreak.
Parsley: Parsley leaves feed the caterpillars of the Black Swallowtail Butterfly and the Anise Swallowtail Butterfly.
Passionflowers: Passionflowers are a great food source for the caterpillars of the Gulf Fritillary Butterfly.
Pine: Pines feed the caterpillars of the Western Pine Elfin Butterfly.
Plumbago: Plumbago feeds the caterpillars from the Marine Blue Butterfly.
Poplar: Poplars produce food for the caterpillars of the Mourning Cloak Butterfly, the Viceroy Butterfly, and the Western Tiger Swallowtail Butterfly.
Saltbush: Different Saltbushes feeds the caterpillar of the Western Pygmy-Blue Butterfly and the San Emigdio Blue Butterfly.
Snapdragon: Snapdragons provide food for the caterpillars of the Common Buckeye Butterfly and the Variable Checkerspot Butterfly.
Sunflower: The different varieties of the Sunflower family feed the caterpillars of a number of butterfly species including those from the Painted Lady, the Dainty Sulphur, the Fatal Metalmark, the California Patch, the Bordered Patch, Gabb's Checkerspot, and the American Lady.
Sycamore: Sycamores feed the caterpillars of the Western Tiger Swallowtail Butterfly.
Thistles: A variety of Thistles provide food for the caterpillars of the Painted Lady Butterfly and the Mylitta Crescent Butterfly.
Violas and Violets: The different varieties of the Violet family provide a good source of food for the caterpillars of the Coronis Fritillary Butterfly, the Callippe Fritillary Butterfly, and the Variegated Fritillary Butterfly.
Virginia Snakeroot: Virginia snakeroot is a good food source for the caterpillar of the Pipevine Swallowtail Butterfly.
Wild Lilacs: Wild Lilacs feed the caterpillars of a number of butterfly species including the Pale Swallowtail, the California Hairstreak, the Hedgerow Hairstreak, the Bramble Hairstreak, the Brown Elfin, the Spring Azure, and the California Tortoiseshell.
Willow: All kinds of Willows provide food for the caterpillars of the Mourning Cloak Butterfly, the Viceroy Butterfly, the Western Tiger Swallowtail Butterfly, Lorquin's Admiral Butterfly, and the Weidemeyer's Admiral Butterfly.
Yuccas: A variety of Yuccas feed the caterpillars of the Yucca Giant-Skipper Butterfly.

More Butterfly and Caterpillar Resources:
For a List of Nurseries and Places that Sell Plants and Plant Products - Click here
For a List of Nectar Plants that Feed Adult Butterflies - Click Here
For a List of Butterfly Species in the Southwest - Click Here
To Learn How to Create your own Butterfly Garden - Click Here