Monday, August 31, 2015

Learning to appreciate a plant I don't like

Primrose willow, Ludwigia peruviana, grows along the shoreline of our lake. It’s a broad, bushy plant dotted with flat, four-petal, lemon-yellow flowers. The flowers bloom almost continually during most of the year.

A bee buzzes by a yellow primrose willow flower

Even though it is a flowering plant, neither my husband nor I care for primrose willow. Something about its sprawling growth pattern and invasive nature prevents adoration. We especially dislike how quickly it takes over the shoreline, blocking views and access to the water. In our eyes, it's a nasty pest, and the Florida Exotic Pest Plant Council agrees.

Primrose willow is a wetland plant that sprawls along the shoreline in front of our house

In 2013, the council listed it among the worst invasive plants. That doesn’t mean it is without admirers, especially among a particular member of the lepidopteron order of insects. The banded sphinx moth, Eumorpha fasciatus, uses primrose willow as a host plant.

A sphinx moth rests during the day and flys at night 

Adult female moths lay eggs on the underside of the plant’s leaves and when the caterpillars hatch, they grow huge on a diet composed entirely of primrose willow leaves.

Most of the primrose willow plants I saw while rowing along the lake's perimeter the other day were at least partially defoliated. It seemed like every bush had at least a few bare branches. Knowing nothing defoliates a plant as effectively as a hungry caterpillar, I rowed close for a better look. Sure enough, I spotted three caterpillars munching their way through the remaining foliage on three different branches of the same plant.

Almost ready to pupate, this banded sphinx moth caterpillar grows huge on a diet of primrose willow leaves

All three were banded sphinx moth caterpillars, distinctive because of their bright-colored, plaid-like patterns on their bodies. While each of the three caterpillars was large — three to four inches long — one looked decidedly different from the other two. Instead of having a red-black-yellow-white pattern, one caterpillar was mainly green, the same color as the leaves, with a series of thin, white swooshes and tiny black and white “eyes” on its sides.

Pretty in plaid, a banded sphinx moth caterpillar nibbles away through a branch of primrose willow leaves

During its caterpillar stage of life, the banded sphinx moth goes through five different stages of development. During each stage, its coloration changes as its body grows longer and thicker. From the look of the long, chubby bodies of the three caterpillars I saw, the two patterned insects had already reached their final stage, and the more green one was close behind.

Can you find the banded sphinx moth caterpillar in its green-colored stage of development?

Soon all three will pupate, that stage in Lepidoptera development when a larva stops feeding and becomes immobile while its body undergoes an intense physical transformation. For that to happen, the banded sphinx caterpillar must climb down the plant on which it has been feeding and crawl into a shallow underground burrow until its metamorphosis is complete and it is ready to emerge as a moth.

Once each caterpillar turns into a banded sphinx moth, it will have attractive A-shaped brown and white wings with a wingspan about four inches wide. It is slightly smaller than a hummingbird and because of its similar size and feeding habits, it is often called a hummingbird moth. The banded sphinx moth has a long furled proboscis that it uncurls to sip nectar from flowering plants, acting as a pollinator in the process. It feeds at dusk and throughout the night and rests during daylight hours on the leaves of plants.

Hummingbird moth sipping nectar from a pickerelweed flower

Learning about the importance of primrose willow to the banded sphinx moth’s lifecycle has tempered my attitude about the plant. While I still don’t like its unruly growth pattern or invasive nature, it helps to know it serves a purpose in nature. Will that stop me from hacking back as many primrose willows as I can from the lake’s perimeter? Probably not, but it does provide a bit of respect for a plant that up until now I saw only as an unworthy pest.


  1. lovely post. Now, if I can only come to terms with that dollar weed.

    1. You and me both! If I come up with anything positive about the lowly (in more ways than one) dollar weed, I'll let you know!

  2. such a lovely approach. Now, if I can only come to terms with the dollar weed in my garden...