Spicebush Swallowtail Caterpillar and its Host Plant

Spicebush swallowtail caterpillar on a leaf

My garden is home to a wide variety of plants, resulting in the presence of both butterflies and their caterpillars. The world of caterpillars and butterflies never fails to amaze me, as each species has its own unique characteristics and behaviors. Over the years, I have developed a particular fondness for the spicebush swallowtail caterpillar. One summer, I noticed the adult form, which resembles the black swallowtail, visiting some flowers in the garden.

Whenever I come across a butterfly in the garden, I make sure to also investigate its caterpillar form and the plants it prefers as hosts. Providing nectar plants for butterflies is great, but we can take it a step further and grow the host plants that their larval form needs to survive.

When I found pictures online of the spicebush swallowtail caterpillar, I immediately fell in love with its unique appearance and fascinating connection with the spicebush host plant (Lindera benzoin). I had not seen any caterpillars in the garden that looked like that before.

Spicebush swallowtail caterpillar
While photographing butterflies in my garden I came across one similar to the black swallowtail. I identified it as the spicebush swallowtail using the iNaturalist app.

At that moment, I made up my mind to locate the host plant spicebush and grow it so I could observe this caterpillar and photograph it. After some searching, we managed to acquire two spicebush plants from a nearby garden store and planted them in our own garden.

It took about two years, but one spring day, I spotted a spicebush leaf that was curled up like a miniature tube. That’s the tell-tale sign! I gently unfurled it and there it was – the spicebush swallowtail!

The Life Cycle of Spicebush Swallowtail Caterpillars

The life cycle of the spicebush swallowtail saterpillar begins with the female butterfly laying her eggs on the leaves of the spicebush plant. These eggs are small, round, and green, blending perfectly with the surrounding foliage. After a short period of time, the eggs hatch into tiny caterpillars, which immediately start feeding on the spicebush leaves.

As the caterpillars grow, they undergo a series of molts, shedding their old skin and revealing a fresh exterior. Each stage of molting, known as an instar, brings about a change in the caterpillar’s appearance. From their initial black and white combination to their later green coloration with unique markings, their appearance at each phase plays a part in how they stay safe from predators.

A young spicebush swallowtail caterpillar in a leaf
During early instars or stages of development, the spicebush swallowtail caterpillar looks like bird droppings to make them less tasty looking to predators.

Adaptations of Spicebush Swallowtail Caterpillars

In nature, evolution fosters innovation, and this is clearly seen in the remarkable diversity of caterpillars. The appearance and behavior of caterpillars have evolved largely as a response to predation pressure. Among their many predators, songbirds possess sharp vision and pose a major threat to caterpillars’ survival. 

Therefore, the survival of caterpillars favors those that can successfully deceive birds. Spicebush Swallowtail Caterpillars have developed several extraordinary adaptations that enhance their chances of survival. One particularly noteworthy adaptation is their ability to imitate bird droppings during their early stages of development. This clever camouflage makes the caterpillars less appealing to birds and other predators.

My favorite form of mimicry and one that it may be most well-known for is its ability to appear as though it’s a snake head. This sets it apart from other caterpillars that typically imitate ordinary objects such as leaves. It showcases false eye spots, known as “snake eyes,” located at the front of its body. To further give the appearance of a snake, the caterpillar also exhibits snake-like behavior if provoked. It will rear up in a threatening snake-like posture.

The false eyes of the spicebush swallowtail caterpillar
As it grows, the caterpillar mimics a snake's head, further enhancing its ability to deter predators.

Another fascinating adaptation of these and other caterpillars I have seen in the garden is the presence of osmeteria. Osmeteria is a pair of forked, orange-colored organs located behind their heads. When threatened, the caterpillars evert these organs, emitting a pungent odor that deters predators. This defense mechanism, along with their mimicry and camouflage, greatly increases their chances of survival.

The Pupa Stage

The spicebush swallowtail caterpillar has a unique way of getting itself ready to become a chrysalis. To ensure a secure grip, it weaves a strand of silk and fastens it to a firm surface. This silk thread is then used to form a loop or “harness” which allows the caterpillar to hang in a vertical position, almost as though it’s lying back into it. 

The back end of the caterpillar is connected to the silk thread, creating a stable and secure structure. This hanging posture is important for the transformation process. The force of gravity helps the caterpillar shed its skin and create the pupal case for protection. By creating the silk loop, the caterpillar can be sure of stability and support during the process of pupation.

Spicebush swallowtail caterpillar in silk harness
The spicebush swallowtail caterpillar turns from green to yellow when it's ready to pupate. It creates a silk harness where it hangs to prepare for its transformation.

How Spicebush Swallowtail Caterpillars Benefit from the Spicebush Plant

The spicebush plant, scientifically known as Lindera benzoin, is a native shrub found in the eastern parts of North America. It plays a crucial role in the life cycle of spicebush swallowtail caterpillars, serving as their primary host plant.

The caterpillars not only use the plant for food but also for shelter by rolling up in the leaves. Their leaf rolling mechanism is one of those amazing feats of natural engineering that’s also so simple that it leaves you speechless. The caterpillar attaches threads of silk to the leaf on either side of the leaf mid-vein and as the silk dries it pulls the leaf around the caterpillar.

I have noticed that it hides in the rolled up leaves in the daytime and comes out at night to eat. The Spicebush provides a continuous food supply for the caterpillars, supporting their growth and development.

The Spicebush plant contains chemicals that make the caterpillars toxic to many predators. These chemicals are stored in the caterpillar’s body, making them unpalatable and potentially harmful to predators. Another defense mechanism, combined with their camouflage and mimicry, that provides the caterpillars with a higher chance of survival.

A curled spicebush leaf

Other Plants that Spicebush Swallowtail Caterpillars Feed On

While the spicebush plant is the primary host plant for the spicebush swallowtail saterpillars, they can also feed on a few other plant species. Sassafras (Sassafras albidum) and Tulip Tree (Liriodendron tulipifera) are among the alternative food sources for these caterpillars. However, the spicebush remains the preferred plant due to its ideal nutritional content and suitability for egg-laying.

The ability of the caterpillars to adapt to different plant species is essential for their survival. It ensures that even in situations where the availability of the spicebush is limited, the caterpillars can still find suitable food sources to sustain themselves until they can locate a spicebush plant.

Predators and Threats to Spicebush Swallowtail Caterpillars

Despite their clever camouflage, spicebush swallowtail caterpillars face numerous predators and threats throughout their life cycle. Birds, spiders, wasps, dragonflies, and other insects are among the common predators that prey on the caterpillars. These predators pose a constant threat, making the survival of the caterpillars a challenging endeavor.

Furthermore, habitat loss and the destruction of the spicebush plant pose a significant threat to the population of spicebush swallowtail caterpillars. Urban development, agricultural activities, and deforestation result in the loss of suitable habitats and food sources for these caterpillars. Conservation efforts are crucial in preserving their populations and ensuring their continued existence.

Chewed and curled leaf of a spicebush.

Interesting Facts about Spicebush Swallowtail Caterpillars

  1. Spicebush Swallowtail Caterpillars have a unique way of communicating with each other. They produce vibrations by rapidly shaking their bodies, which can be detected by other caterpillars in the vicinity.
  2. The Spicebush Swallowtail Butterfly, which emerges from the caterpillar’s pupa, is a sight to behold. With its stunning blue wings and intricate black markings, it is considered one of the most beautiful butterflies in North America.
  3. The Spicebush Swallowtail Caterpillars undergo a remarkable transformation during their pupal stage. Inside the pupa or chrysalis (the transformation stage between the larva and the adult), they liquefy their bodies and reconstruct them into the form of a butterfly. This process, known as metamorphosis, is truly awe-inspiring.
Spicebush swallowtail chrysalis
I have been fortunate to be able to observe and photograph the transformation of spicebush swallowtail caterpillars in my garden into this beautiful and intricate chrysalis. If you plant it, they will come.

Growing Spicebush in Your Garden

If you’re interested in cultivating spicebush in your garden to attract and support the spicebush swallowtail, it’s important to check if it’s native to your region and if this butterfly makes its way to your area. This deciduous shrub is indigenous to the eastern, midwestern, and southern parts of the US.

It thrives in partial shade to full sun and likes moist well-draining soil. In the spring, both male and female bushes produce yellow flowers, although I have noticed mine have never bloomed.

The spicebush shrub

Spicebush typically grows between 6 to 12 feet tall, with a spread of 6 to 12 feet depending on pruning. Female plants may produce red berries that are consumed by birds and other wildlife. To ensure berry production, female flowers must be fertilized by the flowers of a male plant. I must have picked up two male plants because mine have never made berries.

I have read that you can only tell the plant’s sex by looking at details on the flowers. Since the plants weren’t flowering when I bought them, I had no way of knowing.

Although spicebush swallowtail butterflies don’t utilize the berries, multiple plants are needed for berry production. You can propagate Spicebush through collecting and planting the seeds (berries) in late summer or fall. You can also propagate through softwood cuttings taken between July and September using a rooting hormone. This is on my list of things to try.

What native host plants do you grow to support butterflies in your garden?

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Cultivating Nature's Wisdom

I’m a nature photographer and gardener sharing how I created an ecological garden in a small suburban backyard. I also share a few tips for growing and using herbs to craft your own homegrown spice blends.

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