In 1969, in California, a researcher by the name of Robert Stewart sat by a nest of Wilson’s warblers and counted how many times the parents fed their chicks—primarily with caterpillars.

The average was 812 times per day.

Other studies have revealed similar figures. Caterpillars are immensely important to birds and to food webs in general. We can support these food webs in our gardens by growing the plants that host the most caterpillars (the larvae of moths and butterflies). Entomologist Doug Tallamy calls these high-performing plants “keystone plants.”

In the Pacific Northwest, our number-one keystone genus is Salix, the willows. According to the National Wildlife Federation, native willows support 312 moth and butterfly species here.

When I decided to make my garden more wildlife-friendly a few years ago, one of the first things I planted was a willow. I have dry, fast-draining soil and I’m a lazy waterer, so I went with a Scouler’s willow (Salix scouleriana). It’s an upland willow, which means it requires a lot less water than your typical willow. I couldn’t be happier with it.

Despite receiving little irrigation beyond its first summer, my Scouler’s willow has been the fastest-growing thing I’ve ever planted. In 2021, I planted it as a thigh-high start from a one-gallon pot. After two years, it had shot up enough to cast a bit of shade for sitting under on a hot summer day.

After only three years in the ground, it stands 15 feet tall.

My tree should ultimately reach about 30 feet or even taller, but it’s a very upright grower—almost columnar—so it has a small footprint. It’s a great choice for a small, sunny urban garden like mine.

Willows are dioecious, which means each tree has either male or female flowers. Female flowers offer nectar, and male flowers offer both nectar and pollen. My tree bloomed for the first time in 2023, and I was happy to discover it was a male. I knew I’d have pollen for my pollinators.

When the kitten-soft, pussy willow flowers open in March, visitors include early-emerging bumble bees and mason bees. Also, a few mining bees (Andrena spp.) in Oregon are willow pollen specialists, so willow is an essential plant for them.

In general, though, flowers are a bonus with my Scouler’s willow. The main reason I wanted to grow it was for the caterpillars. In only its second year, the first species arrived, and I was there to witness it. I looked on as a western tiger swallowtail butterfly laid three eggs on my tree.

I didn’t have the heart to let my first babies be sacrificial victims, so I took the eggs inside, and I raised the caterpillars on willow leaves. They went into chrysalis in August, but they didn’t emerge in the fall, so I stuck them in the fridge for the winter. In May, I took them out, and a few weeks later, they all emerged.

They were perfect.

According to Merrill Peterson’s outstanding field guide, Pacific Northwest Insects, moth species outnumber butterflies by about ten to one in our area. They do the heavy lifting when it comes to supporting food webs. I’d hoped to find some of the many moth species that feed on willow here, such as the polyphemus moth, the lunate zale, the western eyed sphinx, or the large gray dagger. Alas, nothing so far.

Perhaps the moths need a little more time to find my tree, or perhaps they’ve already found it. I once heard Doug Tallamy address this question after one of his talks.

An attendee said she had planted a native keystone tree in her yard and asked, “Why can’t I find any caterpillars on it?”

Tallamy replied, “Because the birds are better at it than you.”

Here’s hoping the birds are better at it than me, too. After all, if they have to collect hundreds of caterpillars every day to raise their offspring, they’d better be pretty good at it!