Nursery Plants and Their Guests

When trying to create a successful garden, drawing in pollinators is always a huge goal. In order to bring them in but also make sure they can reproduce and thrive, it's important to think about nursery plants.

Nursery plants are those that provide a habitat or resource essential for the growth and development of larvae as they reach maturity. For pollinators like butterflies, this is where they lay their eggs, and the larvae can hatch, eat, and grow until the chrysalis stage.

One great pollinator common on the North American east coast is the Spicebush Swallowtail (Papilio troilus). This fun creature is a dark black butterfly with blue and white markings. The larval form is a bright green caterpillar that sprouts orange 'horns' when it feels threatened. It emulates the look of a snake!

As its name suggests, the Spicebush Swallowtail has a close relationship with the spicebush plant (Lindera benzoin)! The spicebush is the nursery plant for the swallowtail's larvae, providing a location for egg laying, a defense from predators, and a consistent food source. In return for this gift of life, the caterpillar saps the life from the spicebush!

Alright, perhaps not that dramatic, but the caterpillar is very reliant on the spicebush and doesn't really provide any benefit to the plant. Don't fret however, as they will not destroy the spicebush and ruin your garden. If the spicebush isn't too small, then any damage from the caterpillars is quickly recoverable. This is because the spicebush is used to the caterpillar's attack, and has become tolerant to it.

In the summer and early fall, you will find a treat if you search your spicebush for overturned or folded leaves. Hiding inside might just be a little caterpillar!

This is because the caterpillar is spinning silk to fold the leaf over itself. This creates a hiding space safe from aerial predators like birds and wasps. Spicebush Swallowtail caterpillars spend the daytime hanging out in their leaf tube, and emerge during the night hours to consume leaves. Below is a video showing a recently hatched caterpillar hiding!

Planting and guidelines: Generally a low maintenance and adaptable plant. Does best in moist, well drained soil. Full to partial sun is ideal for this plant. Needs to be watered regularly for the first growing season in order to establish its root system. More information can be found here.

Considering that the existence of this bush provides the bug with the ability to survive and reproduce, it makes perfect sense that the Spicebush Swallowtail depends on the presence of this nursery plant for it's existence. I mean, it is named after the plant, so it is fairly obvious. We can see the extent of this bond spatially, since the range of both the plant and the animal are restricted to the temperate east of North America.

Below is a map of observations of both the Spicebush Swallowtail (yellow) and the spicebush (green). Feel free to zoom around and explore the map. Find your garden!

In the map above we can see that the Spicebush Swallowtail and the spicebush are rarely without each other. Since the swallowtail is the one who really needs the partner in this relationship, and the spicebush is pretty nonchalant, we would expect that we'd see areas of spicebush without the swallowtail, and never swallowtail without the spicebush. However, we actually see the opposite in this map. Why is that?

This is because the spicebush is not the only host for the Spicebush Swallowtail. The butterflies actually lay their eggs on multiple kinds of laurel shrubs like sassafras, camphor, red bay, and more. The larvae can survive on these as well. We call this a "generalist" species, meaning that the dependency on a nursery plant is not specific to just one nursery plant, but the relationship is pretty 'general.'

This means that there are a slew of different plants you can choose for your garden that support these little pollinators if you can't get your hands on a spicebush. I'll go through a few.

[1] Sassafras (Sassafras albidium). The unique leaves of this shrub make it easily identifiable and for good reason. This plant has been used for spices and teas for years by humans. Indigenous people used sassafras as a soup thickener.

Planting and guidelines: Low maintenance and hardy tree. Does best in full sun to partial shade. Likes loamy or sandy soil and will not tolerate soggy soil. Needs to be consistently watered for the first growing season so the root system can establish.

[2] Camphor (Cinnamomum camphora). While much larger and more commonly seen as a street tree, it can be a large home to many pollinators. However, you can still grow it as a small shrub in your garden. Be warned, it is not native to the US (originated in China and Japan). Check your states ordinances and planting guidelines before proceeding.

Planting and guidelines: Camphor does best in full sun, and will survive in partial shade, but growth will be reduced. Young trees require regular watering, but older ones can be mostly left alone.

[3] Red bay (Persea borbonia). This flat-leaved shrub is a nice addition to any garden. The commonly used "bay leaf" in cooking is related to this plant. While not native to the US (originated in the Mediterranean), it is not registered as invasive. Many people find success in raising this plant as a potted shrub as well.

Planting and guidelines: Does best in full to partial sun and moist, well drained soil. Semi-frequent watering is needed, especially during dry spells. If growing indoors, they may require direct full sun, or extra heat.

For your enjoyment, I've included a few other videos of the different life stages of the Spicebush Swallowtail.

Happy butterfly gardening!