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Monarch Butterfly Vs Swallowtail (9 Differences)

Monarch butterflies and swallowtail butterflies are two of North America’s most stunningly beautiful insects. Both species can be found in a variety of habitats, ranging from temperate forests to urban areas, and both are common in gardens.

If you’ve discovered their caterpillars, you might be surprised to see how similar they are. Despite having similar-looking caterpillars, these two species are very different in some ways. These could include the color of their wings, their diet, and even the shape of their eggs. This article will help you distinguish between black swallowtails and monarchs by highlighting some of their differences.

Monarch butterfly vs swallowtail

1. Monarch only lays eggs on milkweed

Monarch butterfly egg on a milkweed leaf
Monarch butterfly egg on a milkweed leaf | image by Lorie Shaull via Flickr | CC BY 2.0

Monarch butterflies lay their eggs on milkweed plants so that their young have a food source when they hatch. This is because monarch butterfly caterpillars only eat milkweed during their larval stage.

Milkweed plants contain chemicals known as cardiac glycosides, which help to protect caterpillars from predators such as birds and other predators who may try to eat them while they’re still young. However, black swallowtails are a type of butterfly that feed on plants from the carrot family. This includes carrots, celery, and parsley.

2. Swallowtail caterpillar’s bodies are thicker

Old world swallowtail caterpillar on stem
Old world swallowtail caterpillar on stem | image by Darius Baužys via Flickr | CC BY-SA 2.0

Both species can be difficult to distinguish due to their color similarities, but one key difference between the two is their body shape. Compared to monarch caterpillars, swallowtail caterpillars have thicker bodies.

Monarchs have a more uniform body shape with uniform stripes all over them, whereas swallowtails have a stockier body shape with a hooded head shape. The legs of the swallowtail caterpillar are also longer and thicker than those of the monarch.

3. Swallowtail butterflies have tail-like extensions on their wings

Eastern black swallowtail
Eastern Black Swallowtail Butterfly on pink flower | image by C Watts via Flickr | CC BY 2.0

The swallowtail butterflies are named after their characteristic tail-like extension on their wings. These are called tails because they resemble the tails of swallows.

When predators attack, they usually use their tails to change directions easily. Their hindwings also have a shard edge design, and the color of the tail varies between species, but black swallowtails have mostly black tails.

These characteristics don’t exist in monarch butterflies. They have smooth edges on their hindwings instead.

4.Early instars of swallowtails are black and spiny

Tiger swallowtail caterpillar on stem
Tiger swallowtail caterpillar | Image by jo0ann from Pixabay

Prior to reaching adulthood, both butterflies go through five larval instars. However, the first instars of each species differ greatly from one another.

The first instar of swallowtail larvae appears to be spinier than the mature larvae. They’re mostly black in color, with orange rings at the bottom of each spine and a white center that resembles bird droppings. This enables them to blend in and avoid predators looking for food.

The first instar of the monarch butterfly is very small and gray in color, with a completely black head. They also have small setae and bumps on their bodies.

5. Monarchs tend to live longer

Monarch butterfly
Monarch butterfly | Image by PublicDomainPictures from Pixabay

There are two generations of monarch butterflies: summer and winter. Summer generations have been observed to live for only 2-5 weeks, whereas winter generations have been observed to live for up to 7 months. This is due to the monarch butterfly migrating to central Mexico to hibernate before resuming its active life.

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Black swallowtails, unlike monarchs, don’t migrate and can only survive in warmer climates, so they don’t live as long. Instead, they spend the winter as pupa within a chrysalis. Adult butterflies have a lifespan of 6 to 14 days, but some can live for up to a month.

6. Black swallowtails have yellow dots on their stripes

Black swallowtail caterpillar
Black swallowtail caterpillar | image by Dean Morley via Flickr | CC BY-ND 2.0

Black swallowtail caterpillars are mostly greenish yellow with black and white stripes, with yellow or orange dots on the black stripes. The stripes on their body are also thick in size.

Monarch butterflies, on the other hand, have stripes that are thinner and more uniformly shaped than those of swallowtail butterflies. They also have the same yellow, black, and white stripes as black swallowtails but lack the orange or yellow dots.

7. Monarch caterpillars have tentacles on both ends

Monarch caterpillar on stem
Monarch caterpillar on stem

Monarch butterfly caterpillars have tentacles on the top and bottom of their bodies. These serve two functions for the caterpillars.

The tentacles guide the caterpillar and act as sensory organs to help them find food and identify predators. The ones on their back are also used for self-defense. This tricks predators into thinking the insect’s back is its head.

The larva of the black swallowtail has fork glands on its head called the osmeterium. This is usually kept hidden and is only used for self-defense. When the caterpillars sense danger, they’ll release these orange horns. These glands will emit a foul odor, scaring off predators.

8. Swallowtails have a different color at the end of their hindwings

Laurel swallowtail
Laurel swallowtail | image by Renee Grayson via Flickr | CC BY 2.0

Another distinguishing feature of black swallowtails is the color of their hindwings. Aside from the tails, the end of their hindwings has a powdery blue color and small eyespots. They also have large white spots on the edges of their wings.

Monarchs don’t have any other color than orange and black on their hindwings. You can also see white spots on the edges that are smaller than that of the swallowtails.

9. The shape of their eggs

Monarch butterfly egg on a milkweed
Monarch butterfly egg on a milkweed | image by Lorie Shaull via Flickr | CC BY 2.0

Monarch butterfly eggs are typically oval in shape and white or off-white in color. You can also see some ridges on the sides of their eggs.

The eggs gradually become darker in color as the larva grows inside until it hatches. Their eggs are usually found attached to the underside of the leaves of the milkweed plant.

On the other hand, black swallowtails lay their pale yellow eggs on carrot family plants. They usually attach their rounded-shaped eggs to the tops of these plants’ leaves.