What Do Swallowtail Butterflies Eat? Host Plants to Nectar
What do swallowtail butterflies eat depends entirely on which life stage you're looking at. Caterpillars in the family Papilionidae chew leaves from a narrow list of host plants, while the winged adults switch almost completely to flower nectar. That single diet change, from foliage to nectar, drives where you'll find each stage and which plants are worth adding to a garden.
Four Stages, Two Very Different Diets
Swallowtails go through complete metamorphosis: egg, larva, pupa, and adult. The egg and pupa stages don't involve feeding at all. Females glue eggs singly onto a host plant leaf, and the caterpillar that hatches is on its own food source from day one. The pupa, or chrysalis, doesn't eat; it's a resting stage where the tissue reorganizes into an adult body.
Egg Stage
A female swallowtail lays each egg directly on a plant her species' caterpillars can digest. This choice matters more than almost anything else in the life cycle: a caterpillar that hatches on the wrong plant will starve within days because it can't move far or switch food sources.
Larva Stage
Newly hatched caterpillars eat leaf tissue from their host plant almost continuously, molting through five instars as they grow. Early instars often eat only small notches out of a leaf edge; later instars can strip whole leaves. All of that tissue gets converted into the fat and protein reserves the caterpillar needs to survive the pupal stage, when it can't feed.
Pupa Stage
Inside the chrysalis, the caterpillar's body breaks down and reorganizes into the adult butterfly. No feeding happens here; the insect runs entirely on reserves built up during the larval stage.
Adult Stage
Once a swallowtail ecloses from its chrysalis, its mouthparts are a coiled proboscis built for liquid, not leaves. Adults feed on nectar, and some also sip minerals from mud puddles.
What Adult Swallowtails Feed On
Adults of both sexes take nectar from a wide variety of native and exotic garden plants, using the long proboscis to reach into blooms other insects can't access. In the process, pollen collects on their head and wings and gets carried to the next flower.
Nectar Plants They Favor
Swallowtails aren't picky about a single species, but a few garden plants come up again and again as favorites:
- Butterfly bush (Buddleia): Long, nectar-heavy flower spikes that stay in bloom for weeks.
- Milkweed (Asclepias): Best known as the monarch's host plant, but its nectar also draws swallowtails.
- Coneflower (Echinacea): A drought-tolerant native that keeps producing nectar through summer heat.
- Lantana: Clustered blooms in orange, pink, and yellow that swallowtails visit repeatedly.
Feeding and Mating Behavior
A few behaviors show up consistently in the field:
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Territorial males: Males often patrol or perch near nectar-rich patches to intercept females, chasing off rival males that enter the area.
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Color preference: Swallowtails are drawn more strongly to yellow, pink, and purple blooms than to less visually saturated flowers.
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Mud-puddling: Groups of males gather at damp soil, sand, or gravel to drink water and draw in salts and minerals that aren't available from nectar alone.
What Caterpillars Eat: Host Plants by Species
Unlike the adults, caterpillars are tied to a short list of host plants, and that list is different for each species.
Host Plant Examples
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Eastern Tiger Swallowtail (Papilio glaucus): Common host plants include tulip tree (Liriodendron tulipifera) and wild black cherry (Prunus serotina); in peninsular Florida, sweetbay magnolia is the preferred host instead.
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Western Tiger Swallowtail (Papilio rutulus): Found through western North America, where its larvae feed mainly on willow and cottonwood leaves.
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Black Swallowtail (Papilio polyxenes): Larvae utilize a variety of herbs in the carrot family (Apiaceae), including parsley, dill, fennel, and Queen Anne's lace, which is why gardeners sometimes call the caterpillars parsleyworms.
Why the Nutrients Matter
The leaf tissue caterpillars eat has to cover three jobs at once: build new muscle and cuticle as the caterpillar grows through five molts, fuel the energy cost of that growth, and stockpile the reserves that carry the insect through the non-feeding pupal stage. A caterpillar that's forced onto a poor-quality host, or too little of it, often emerges as a smaller, weaker adult.
Staying Off the Menu
Swallowtail caterpillars have their own defenses against being eaten while they eat. Young larvae of several species resemble bird droppings, which is enough to make most predators pass by. Later instars of some species carry eyespots that make the front of the body look like a small snake's head, and nearly all swallowtail caterpillars have an osmeterium, a forked orange gland behind the head that pops out and releases a foul smell when the caterpillar is disturbed.
Growing Plants for Both Stages
Because caterpillars and adults eat completely different things, a garden that only offers nectar flowers will attract passing adults but never host a full generation. Supporting the whole life cycle means planting for both stages.
Building a Garden That Covers the Whole Life Cycle
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Plant region-appropriate host plants: Parsley, dill, and fennel work for black swallowtails almost anywhere in the US; tulip tree or wild cherry work for eastern tiger swallowtails where there's room for a tree.
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Stagger bloom times: Mixing early, mid, and late-season nectar plants keeps food available across the whole adult flight period instead of one short burst.
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Skip the pesticides: Broad-spectrum insecticides kill caterpillars along with whatever pest they're aimed at, and residues on nectar can harm adults too.
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Leave some shelter: Shrubs or a hedge give adults a place to rest overnight and caterpillars a spot to pupate away from open ground.
The Diet Shift Is the Whole Point
The move from leaf-eating larva to nectar-feeding adult isn't a minor detail, it's the reason swallowtails need two different kinds of plants to complete a single generation. A yard with both host plants and nectar sources does more for local populations than nectar flowers alone ever will.
