Butterflies and Larval Food Plants

The presence of butterfly larva food plants generally determine local butterfly populations.


At the start, new butterfly gardeners concentrate on attracting adult butterflies by adding nectar plants to their landscapes. But curiosity and logic soon drive them to wonder about the other side of the life cycle, and that’s where the fun really begins.

Photo courtesy Fotolia/abet

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WARNING! Butterflies can be addictive!

So say many new books on butterfly identification, and the number of "butterfliers" to join the sport in the last decade seems to confirm this. A new style of field guide that allows identification on the fly, rather than requiring the butterflies be netted and killed, is partly responsible. Anyone who has used a bird guide will be comfortable with this method, and with using a pair of short-focusing binoculars that allows you to study a butterfly as close as your foot without scaring it away.

At the start, new butterfly gardeners concentrate on attracting adult butterflies by adding nectar plants to their landscapes. But curiosity and logic soon drive them to wonder about the other side of the life cycle, and that’s where the fun really begins.

Gardeners and other plant lovers often find the study of butterflies particularly rewarding because it offers fascinating glimpses into why plants are the way they are. Like most herbivores, butterflies have a preferred meal plan — in fact, many species are so finicky about their choice in food plants for their caterpillar stage that their survival rates rise and fall on the success of a single plant species. The coevolutionary dance between plant and insect is an amazing story of defensive strategies attempted, overcome, improved and overcome once again.

Plants "retaliate" for being chomped on by developing special poisons or distasteful chemicals. We humans have many reasons to be grateful for this process — the herbivore pressure on plants has led to wonderful adaptations, both medicinal and flavorful. Mints, oregano, spicy nasturtium leaves and pine resin are good examples. Most of the aromatic smells, unique tastes and medicinal properties we enjoy in plants came about as defenses. Butterflies are only the visible tip of the iceberg when it comes to the world of insect herbivores driving these botanical experiments — but they are so wonderfully visible!

Plants' chemical-defense plans generally work, but eventually an insect comes along that finds a way to neutralize the poison, or better yet, put it to a good use. The relationship between monarch butterflies and milkweed is a celebrated example. The poisonous glycosides in milkweed repel most herbivores. But monarch caterpillars not only eat the leaves, they harmlessly store the glycosides on into adulthood. Birds learn quickly to avoid these brightly colored butterflies after the first vile taste.

Over time, as the plant ramps up the concentration of the compounds, the insect eating it adapts. But success comes at a cost — eventually, the butterfly becomes dependent on those compounds, which it needs to trigger both egg-laying behavior and larval feeding. Apollo butterfly larvae eat stonecrop and store for defense a compound from it called sarmentosin. Red admirals nibble safely on nettle leaves. Pearl crescents need asters. Fritillaries only eat violets (though you won’t catch them at it since the caterpillars retreat into the ground during daylight). Skippers cue in on grasses. Cabbage whites eat, well, cabbages. (Leave the Bt spray off one of your cabbage or broccoli plants to encourage those delightful butterflies.) And so it goes, for most species.

With the exception of a few butterfly species that migrate in, it is the presence of larval food plants that generally determine local butterfly populations. These plants are almost always native to the area. If your yard and garden consist of mowed lawn and non-natives, you probably aren’t offering much larval habitat. You can remedy that by dedicating an area to host plants — a good field guide will help you figure out what plants your local butterflies use. Leaving parts of your property in a wild, untended state is probably one of the best things you can do for these beauties. And unless you have a specific pest problem to control, ignore gardening advice that says to do an autumn cleanup to remove all dry leaves and perennial stalks — it is just those protected places where caterpillars and chrysalides spend the winter. Not only will you have better butterfly habitat — you will have more time to sit still and be enchanted by the spectacle of butterfly life. 

Marvelous Milkweed

You can attract monarch butterflies to your yard by planting a patch of milkweed, a very easy-to-grow native perennial that produces seed pods with those downy white tufts many of us love to set free on the wind. And you’ll get a bonus if you grow milkweed: The young shoots and flower buds are edible, plus the unique fluffy floss in the mature seed pods makes a superb alternative to expensive goose down for use in insulated vests, jackets and even comforters.

You can boil young milkweed shoots and leaves for an asparagus-like vegetable. (Avoid mature leaves and stalks, which are bitter.) Young flower buds and very young pods have a pealike flavor. The flowers can be used as a thickener for soups and can be boiled down to make a sugary syrup.