Blog module icon

MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

Need Help?
For tips on subscribing, searching, and commenting, please visit our blog FAQ page.

View All Posts

Aug 01

Does it Pass the Test as a Garden Pest?

Posted on August 1, 2017 at 10:15 AM by Ann Vallee

by Keith Bancroft, Water Conservation Specialist Supervisor

CA Fuschia
California fuchsia in Harvey’s Garden,Tiburon (photo by Keith Bancroft)
A few weeks ago, I was perusing the aisles of my local nursery when I came across a dozen or so containers of California fuchsia. This is a plant I have wanted to add to my garden ever since I saw a wonderful patch of it in Harvey’s Garden at Blackie’s Pasture last year.

As I was sorting through the containers to find the healthiest looking specimens, I noticed a very large green caterpillar on one plant. I didn’t know what type of caterpillar it was, but I decided to take it (and the fuchsia it was on, of course) home to my garden. When I pointed out the caterpillar to the sales person she took a quick look at the horn on its tail and said, “Oh, you should kill that—it’s a tomato hornworm.”

Top: Tomato hornworm (photo by Oreen Delgado). Bottom: White-lined sphinx moth caterpillar (photo by Keith Bancroft)
I’ve never had hornworms on my tomato plants, and I didn’t have any desire to bring one home to take up residence, but I was hesitant to squash this little guy before knowing definitively just what it was. So, once I got back home, I searched the internet and found that, although it was a hornworm, it was not a tomato hornworm. It didn’t have the tell-tale white stripes across its body.

At that point, I knew what it wasn’t, but I still didn’t know what it was. After a few more minutes of searching, I found it appeared to be the caterpillar of a white-lined sphinx moth. This hornworm doesn’t usually cause any significant concerns for most gardens (unless their numbers are excessive). As an adult, this moth is sometimes mistaken for a hummingbird as it hovers over flowers drinking nectar, and thus its nickname “hummingbird moth.”

This experience demonstrates the importance of recognizing that there are a variety of critters in our gardens—some beneficial, some harmful—and it’s often difficult to identify or otherwise tell the difference between them. I believe it’s best to err on the side of caution and make sure you know what you’re dealing with before making the decision to dispatch them, lest you become the biggest harmful critter in your garden.

A few hours after completing my internet detective work, I went out to plant the fuchsia and found the caterpillar was gone. Perhaps a bird made a meal of it. I prefer to think it crawled away to start the next stage of its life—they burrow just below the soil's surface to pupate and then reemerge as a moth. I’ll be paying closer attention to the hummingbirds in my garden over the next few weeks, and I hope to find an imposter amongst them.


Anonymous User
August 4, 2017 at 3:54 PM
Keith, you might explain exactly how you "searched the internet" to identify this fella from your picture. Cute pictures of the hummingbird moth.
Anonymous User
August 4, 2017 at 4:44 PM
Epilobium canum = California fuchsia
Keith Bancroft
August 7, 2017 at 8:50 AM
I first Googled "tomato hornworm" and looked at the "image" results. It took less than a minute for me to realize the caterpillar was not a tomato hornworm. I then Googled various search terms - "green hornworm on fuchsia", "green hornworm with yellow spots", etc. - and then scrolled through many pages of "image" results until I found something similar. There are many variations of hornworms, even for the same caterpillar, so it took a good 15 minutes of visiting various pages before I was reasonably sure I had the correct ID.
Anonymous User
August 8, 2017 at 10:55 AM is an excellent resource as well

Leave your comment

You may log in before leaving your comment,
or submit anonymously