The monarch, up close

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1. 1Head capsuleA hard helmet covers the head. It can't stretch, so to grow bigger the caterpillar crawls out of it and makes a new one.
2. 2Six simple eyesSix tiny eyes sit on each side of the head. They tell bright from dark, but a caterpillar can't see clearly.
3. 3Front feelersThe long black whips are feelers for touch. They are not antennae, and they can't sting.
4. 4Back feelersA shorter pair sits at the back end. They feel touch too.
5. 5Six true legsSix jointed legs up front, like every insect has. They hold the leaf steady while the jaws chew.
6. 6Ten soft prolegsTen soft, stumpy legs on the belly and tail. They aren't real legs, and the butterfly won't have them.
7. 7Tiny hooksEach soft leg ends in a row of tiny hooks, like Velcro, so the caterpillar can hang on in the wind.
8. 8Breathing holesA row of tiny holes runs along each side. The caterpillar breathes through them, not through its mouth.
9. 9Warning stripesBold black, white and yellow stripes tell birds, "I taste bad!" The bad taste comes from milkweed.
10. 10Jaws and spinneretStrong jaws open sideways like scissors to snip leaves. A tiny spout below the mouth pulls out silk.
11. 11AntennaeTwo tiny stubs beside the jaws. They help the caterpillar smell its way to milkweed.

Sources: Oberhauser & Kuda, A Field Guide to Monarch Caterpillars (University of Minnesota, 1997); USDA Forest Service, Lepidoptera of the Pacific Northwest, ch. 3; Monarch Joint Venture. Fact not pictured: two long hairs behind the head sense sound, so caterpillars can "hear" (J. Exp. Biol., 2019).

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1. 1Food pipeChewed leaf bits slide down a short food pipe from the mouth into the stomach.
2. 2StomachThe stomach is the biggest thing inside. It fills most of the body and digests leaves almost nonstop.
3. 3HindgutThe last part of the tube takes back water and packs the leftovers into little poop pellets called frass.
4. 4Silk gland (one of a pair)A long tube that makes liquid silk. Its twin is on the other side. The silk becomes thread as the caterpillar pulls it out of its spinneret.
5. 5HeartThe heart is a long tube along the back. It squeezes blood forward toward the head, and the blood seeps back.
6. 6Belly nerve cordA nerve cord runs along the belly like a string of beads. Ours runs along our back instead.
7. 7Fat bodyCreamy packing tissue stores food energy. It's the lunchbox for the chrysalis, which can't eat.
8. 8Air tubesSilvery air tubes branch from the breathing holes to every part of the body, bringing air straight in.
9. 9Wing budsTiny flat pockets of cells hide inside the caterpillar. They are the start of butterfly wings.

Sources: Oberhauser & Kuda (1997); USDA Forest Service, ch. 3; NC State University, General Entomology; Monarch Joint Venture.

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1. 1Silk padBefore changing, the caterpillar spins a little silk mat, grabs it with its back legs and hangs upside down in a J.
2. 2Hook stalkA black stalk at the top, covered in tiny hooks, holds on to the silk like Velcro.
3. 3Chrysalis skinA chrysalis isn't spun or built. It's the caterpillar's own new skin, which hardens into a green case.
4. 4Gold bandThe gold isn't real gold. Stacks of see-through layers bounce light like a soap bubble. Nobody knows for sure why it's there.
5. 5Folded wingThis big smooth patch is a folded wing. The wings are already there, pressed flat under the skin.
6. 6Leg, tongue and antenna casesThin ridges show where the antennae, tongue and legs lie folded, like clothes packed in a suitcase.
7. 7Eye bumpNear the bottom, a smooth bump shows where the big butterfly eyes are forming.
8. 8First days: breaking downInside, many caterpillar parts break down into a soft, gooey mix. But it isn't all liquid.
9. 9Air tubes, keptThe air tubes stay. In painted lady chrysalises, X-ray scans showed them about 12 hours after the chrysalis formed.
10. 10Middle: buildingStarter cells use that gooey food to build new parts: wings, long legs, big eyes and a two-part tongue. The two halves zip together after the butterfly comes out.
11. 11Last day: see-throughA day before the butterfly comes out, the case turns clear. You can see the orange and black wings inside!

Sources: Monarch Joint Venture; Monarch Watch; Lowe et al., J. R. Soc. Interface (2013) on X-ray scans of painted lady chrysalises; Blackiston et al., PLoS ONE (2008) on memory through metamorphosis. The "it all turns to liquid" line in some popular articles is a myth.

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1. 1Compound eyesEach big eye is made of thousands of tiny eyes working together. Butterflies can even sense which way light waves are traveling, something we can't see.
2. 2Clubbed antennaeThe knobbed feelers smell flowers and mates. They also hold tiny clocks that help migrating monarchs steer by the sun.
3. 3Curly tongueThe tongue is a long drinking straw, rolled up like a party blower. It uncurls to sip nectar.
4. 4PalpsTwo furry pads beside the face cover the rolled-up tongue and help sense the world.
5. 5ThoraxThe middle part is the engine room, packed with muscles that work the wings and legs.
6. 6Four wingsA butterfly has four wings, not two. The front pair is bigger and pointier; the back pair is rounder.
7. 7Wing overlapThe front wing rests on a flap of the back wing. No hooks: they overlap and flap together as one.
8. 8Tiny front legsMonarchs have six legs, but the front two are tiny and tucked up, so they look like they have four.
9. 9Tasting feetMonarchs taste with their feet! A mother taps a leaf to check it's milkweed before she lays an egg.
10. 10ScalesThe colors come from tiny scales laid like roof shingles. "Lepidoptera" means "scale wings".
11. 11VeinsThe black lines are veins, tubes that stiffen the wing. A new butterfly pumps fluid through them to open its wings.
12. 12Male scent spotBoys have a black spot on each back wing, right on a vein. It's made of special scent scales.
13. 13AbdomenThe long back section holds the stomach, and in mothers, the eggs.
14. 14ClaspersBoys have two little claspers at the tip of the tail, for holding on when they pair up.
15. 15Orange-and-black warningBright orange and black say "Don't eat me!" Monarchs keep milkweed poison in their bodies, so a bird that tries one gets a nasty taste. A few birds eat them anyway.

Sources: Monarch Joint Venture; Monarch Watch, Sexing Monarchs; Merlin, Gegear & Reppert, Science (2009) and Guerra et al., Nat. Commun. (2012) on the antenna clock. Not pictured: a new butterfly's tongue comes out in two halves, which it zips together soon after emerging.

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1. 1Flower ballLots of little flowers grow from one point, like the spokes of an umbrella. The round cluster is called an umbel.
2. 2Petals cup upwardOn most milkweeds the petals fold back. On antelope horns they cup upward around the middle, like a little bowl.
3. 3HoodsFive scoop-shaped hoods hold sweet nectar. Bees and wasps clamber over them to drink.
4. 4Center columnThe flower's middle is one joined-up column, where the pollen parts and the seed-making parts are fused.
5. 5Pollen clipMilkweed pollen isn't dust. It comes in two waxy bags hanging from a tiny clip, like saddlebags.
6. 6The clipThe tiny dark knob joining the two bags is the clip. It grabs an insect's foot as the insect pulls its leg out of a slit in the flower. The flower close-up doesn't show the slits.
7. 7Pollen bagsEach waxy bag is packed with pollen. Slipped into another flower, it starts the seeds.
8. 8Along for the rideThe clip hitches a ride on a bee's leg. Its arms twist as they dry, so the pollen only fits the next flower.
9. 9Seed podThe curved green pod looks like an antelope's horn. That's where the name comes from!
10. 10SeedsInside, flat brown seeds are packed tight, overlapping like fish scales.
11. 11Silk parachuteEach seed wears a silky parachute. When the pod splits, the wind carries the seeds far away.
12. 12Milky sapBreak a leaf and white, sticky sap oozes out. It's poisonous, and it can glue a tiny caterpillar's jaws shut.
13. 13Caterpillar notchBig caterpillars bite a notch in the leaf stalk first. That drains the sap away, so the leaf is safer to eat.
14. 14TaprootA thick root reaches deep underground. It helps the plant survive dry summers and grow new stems.

Sources: Lady Bird Johnson Wildflower Center; Monarch Watch milkweed profiles; Native Plant Society of Texas; Hastings et al., PeerJ (2026) on latex and toxins; Dussourd & Eisner, Science (1987) on leaf-notching; MacIvor et al., Ecol. Evol. (2017) on which insects carry the pollen.

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