Who Pooped on My Lemon Tree? Meet the Swallowtail Caterpillar

I’ve been checking my lemon tree lately because I kept seeing other Southern California gardeners posting pictures of swallowtail caterpillars on their citrus.

And I finally found one! 🍋🦋

At first glance, though, you might not think “butterfly.”

You might think bird poop.

And that's exactly the point.

Why does it look like bird poop?

Young swallowtail caterpillars of several species have evolved some pretty remarkable camouflage: they resemble bird droppings.

It may not be glamorous, but looking like something a bird definitely doesn't want for lunch is a pretty clever survival strategy. The Xerces Society describes this bird-dropping mimicry as a defense that likely helps make caterpillars less appealing to predators.

Nature is amazing—and occasionally has a sense of humor.

Why is it on my lemon tree?

A butterfly garden isn't just about flowers.

Adult butterflies need nectar plants, but their caterpillars need host plants—the particular plants they can actually eat while developing. Many butterfly species can use only a relatively limited group of plants as caterpillars.

And for some swallowtails, citrus is on the menu.

Here in California, the native Anise Swallowtail (Papilio zelicaon) can feed on citrus as well as plants such as fennel. UC IPM notes that the caterpillars may eat tender citrus foliage but rarely cause economically significant damage to mature citrus trees.

Giant Swallowtails (Papilio cresphontes) also use citrus as a host plant and are among the butterflies documented in Orange County. My guess is that the little one I found is a Giant Swallowtail, but I'm going to keep watching as it grows.

So when I find a caterpillar munching away on an established lemon tree, my first instinct isn't to reach for a pesticide.

It's: You can eat as much of my lemon tree as you want, little one. 💚

The fact that I don’t spray my plants with pesticides is exactly why that caterpillar is here. Sometimes we work so hard to prevent damage to our plants that we don't realize what else we're preventing.

A few chewed leaves can be a good thing

We tend to judge the health of a garden by how perfect everything looks.

No holes. No chewed leaves. No bugs.

But a garden that supports wildlife may look a little different.

A chewed leaf can mean that a plant is doing something beyond looking pretty—it's participating in an ecosystem.

This reminds me of something Doug Tallamy teaches: when insects are eating our plants, what we see as “damage” can actually be evidence that the plant is being used as part of the food web.

That's one reason I'm increasingly interested in designing landscapes that don't just survive in Southern California, but actually provide habitat.

The Xerces Society makes an important distinction for butterfly gardening: nectar flowers feed the adults, but host plants support the caterpillars that make the next generation of butterflies possible.

Sometimes helping butterflies means being willing to share your plants.

I'm happy to share my lemon tree. 🍋🐛🦋

Want to learn more?

The North American Butterfly Association's swallowtail resources are a good place to explore the different swallowtail species found in North America.

The Xerces Society also has extensive information about creating habitat for butterflies, moths, and other beneficial insects.

And if you have citrus growing in your Southern California garden, take a closer look at the leaves.

You might have a future butterfly hiding in plain sight.

🌿 I observe.
📚 I learn.
🤝 I help.

🌿 Helping Southern California homeowners create beautiful, sustainable landscapes that thrive.