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Recently, someone emailed me and asked "Can you fill me in on this ‘host’ thing?" I've heard "What is a host plant?" many times. When I tell them it’s a plant grown to feed caterpillars, often I get a shocked response. The usual reaction to many gardeners is to use pesticides to kill all critters that are eating their plants. Many just don’t make the connection between caterpillars/butterflies. I have to explain to them WHY I plant stuff for caterpillars. As I explain, often I see the ‘light bulb’ come on when they realize what I’m doing. Often, I hear "OH NO! All these years, I’ve been killing Black Swallowtail caterpillars on my Parsley?" Even the nicknames some of the caterpillars get are not appealing: ‘Parsley worm’ for the Black Swallowtail, and ‘Orange Dog’ for the Giant Swallowtail. People just don’t pay enough attention to the caterpillars.

This is not an article on caterpillars (maybe next time). Today, I want to write about host plants. Caterpillars are very particular eaters, and have very specific food requirements. Some will use a variety of broadleaf trees for a host plant, while others will only utilize one variety of a plant. Whichever is the case, there is no substitute for a caterpillars food requirements. You can’t just throw in some grass or spinach and expect the caterpillar you just found to survive. Also, a caterpillar that eats milkweed (Monarch) cannot switch to eating Passionvine. You’ve got to know 1.) what kind of caterpillar it is, and 2.) what it’s host plant is. If you don’t know these things, please leave the caterpillar alone and let Ma Nature care for it.

A butterfly will lay her eggs on the host plant. Some lay groups or masses of eggs on one leaf, while others will only lay one egg per plant to ensure enough food for her caterpillar. Normally, they will only lay on the host plant, but I’ve seen a Gulf Fritillary, seemingly in a laying frenzy, lay on a red hot poker (NOT a host plant). If you want the butterflies to come to your garden and STAY, you’ve got to provide for the caterpillars.

What ARE host plants? Here is a ‘generic’ list I found, along with the species that eat them:
Achillea millefolium (yarrow). Painted Lady
Anethum graveolens (dill). Black Swallowtail; Anise Swallowtail
Angelica spp. Black Swallowtail; Anise Swallowtail
Artemesia absinthium (wormwood). Painted Lady
Artemesia dracunculus 'sativa' (French tarragon). Oregon Swallowtail
Borago officinalis (borage). Painted Lady
Carum carvi (caraway). Black Swallowtail; Anise Swallowtail
Dictamnus spp. (gas plant). Giant Swallowtail
Foeniculum vulgare (fennel). Black Swallowtail; Anise Swallowtail
Glycyrrhiza spp. (licorice). Silver Spotted Skipper
Helichrysum angustifolium (curry plant). Painted Lady
Humulus lupulus
(hops). Gray Hairstreak; Comma; Question Mark; Red Admiral
Levisticum officinale
(lovage). Black Swallowtail; Anise Swallowtail
Melissa officinalis (lemon balm). White Peacock
Mentha spp. (mint). White Peacock, Painted Lady
Petroselinum crispum (parsley). Black Swallowtail; Anise Swallowtail
Pimpinella anisum (anise). Black Swallowtail; Anise Swallowtail
Ruta graveolens (rue). Black Swallowtail; Giant Swallowtail. Warning: oils can burn sensitive skin; wear gloves when handling.
Salvia spp. (sage). Gray Hairstreak; Painted Lady; West Coast Lady
Symphytum officinale (comfrey). Painted Lady
Tanacetum vulgare (tansy). Painted Lady
Tropaeolum majus (nasturtium). Cabbage white
Viola odorata (sweet violet). Fritillaries

They seem to have their favorite varieties according to geographical location. Black Swallowtails, for example, prefer Italian flat leaf Parsley in my garden, while they prefer Dill in another’s, or curly Parsley still in others gardens. According to Marc and Maria Minno in their book Florida Butterfly Gardening, once a caterpillar starts to feed, it becomes programmed to that host species. Switching a Tailless Swallowtail larva from one species of Aristolochia (Pipevine) to another may result in slower growth, smaller size, or starvation. I like to plant several varieties of host plant in my garden, giving the butterflies AND caterpillars a choice. For example, I have parsley, dill, fennel, and rue for the Black Swallowtails. I’ve found them on all four types, but mostly on the parsley.

As you can see from the list above, herbs are great host plants. I say that because, not only are they loved by the caterpillars, the flowers are often great nectar plants for the butterflies. AND most herbs are ‘no brainers’ to grow too! All they need is lots of sunshine, well drained soil, and NO pesticides. Many trees too, like Magnolia, Willow, and Oak will be welcomed. Sometimes, ‘weeds’ are best: Spanish Needle, Pepper Grass, Plantain, Mock Bishop’s Weed, and even crabgrass are great host plants.

To find out which host plants you’ll need in your garden, go to Butterflies of North America page and click on your state. Then look at the info on the various butterflies and figure out which appear in your garden. Read up on the host plants of these butterflies, then plant it. It’s like a jigsaw puzzle, once you put the pieces together, you’ll have ‘Flying Flowers’ all over your yard.

What is a butterfly garden?  Jan 2000

Companion planting

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