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Life on a Dogwood

—This article by Dick Fisher first appeared in our WildforaRI, Spring 2021

We are by now aware of the importance of pollinators in our ecosystem to promote diversity, fertilize native and food crop plants, and take their place in the food web. Pollinator gardens are the rage and for good reason. But the story does go deeper, so let’s start with a nice summer day last August.

Passing by an actively growing red-twig dogwood, aka red osier dogwood (Swida sericea), it was obvious some leaves were missing and stems were wiggling. Indeed the leaves of several small branches had been stripped and were being devoured by a large number of gray, striped, clamoring caterpillars. Although the shrub was small, less than one percent of it seemed affected. The caterpillars remained bunched together and confined themselves to the several adjacent twigs. Over the next few days their numbers decreased, and then they were gone; the red-twig dogwood did fine.

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This was a red-humped caterpillar (Schizura concinna) and is just one of 113 species listed in the National Wildlife Federation database that feed on the dogwoods in our area.1 Several species are limited to dogwoods only but most, like Schizura, feed on a multitude of native trees and shrubs.2

Lifecycle

The red-humped caterpillar is the larval stage of a small brown inconspicuous moth. The adult moth emerges from the pupa in the spring or early summer and lives only seven or so days during which the female deposits small yellow eggs on the underside of the host plant’s leaves. The eggs hatch in about two weeks to begin the larval stage as caterpillars and begin eating, perhaps increasing their mass one thousandfold over one and a half months until they are mature.2

As they grow they molt, shedding the outer cuticle and forming a new covering. Between molts they are known as “instars.” There are multiple instar stages as the caterpillar grows. The first instar is the larval form that hatches from the egg, and the final instar forms the pupation cell. Most butterflies spin a cocoon in which the pupa develops while moths usually develop an unprotected pupa cell. The red- humped caterpillar’s final instar drops into leaf litter and soft ground beneath the host plant and spends the winter in a pre-pupa stage. Pupation begins after the winter and ends with the emergence of the adult moth. In our area there is usually just one or perhaps two cycles per year.2

The red-humped caterpillars were not alone last summer. The dogwoods here hosted at least three other dependent species including the rusty tussock moth (Orgyia antiqua), the dogwood sawfly (Macremphytus tarsatus), and the yellow sawfly (Macremphytus lovetti). Sawfly larvae look and behave much like caterpillars but differ in some fundamental anatomical features such as the number of appendages or eyespots.3 True caterpillars belong just to butterflies and moths, but the life cycles of both the true caterpillars and sawfly larvae mentioned in this article are similar as is their dependence on the dogwood.

Diversity

We see these caterpillars and larvae for just a short time, but it is the time when they are most vulnerable. Schizura concinna, like the others, is a food source for something at every stage of its life cycle. The eggs are attractive to other insects, the adult moth is not a beautiful butterfly but is food for birds, and the pre-pupa and pupa stages are prey for soil organisms. The larvae, being highly visible, are at high risk, so much so that they have developed several defensive strategies. When disturbed these particular caterpillars show a collective warning display by thrashing about in unison, and they excrete an offensive fluid containing formic acid.3 Despite that behavior, they slowly disappeared over the next week or so, and I am not sure where they went. Perhaps some dropped into the leaf litter to begin their next stage, but many were still small and I suspect became part of the food chain for local birds.

In addition to our red-twig dogwood, two other dogwood species grow here: alternate-leaved dogwood (Swida alternifolia) and gray dogwood (S. racemosa). They flower and require pollination to produce seed. If not the red-humped moth then maybe another adult stage from the 113 species they host will help out. But they also have many non-lepidoptera pollinators including bees, wasps, and, yes, sawflies. The sawfly adults look like a cross between a fly and a wasp, they do not sting, and they can pollinate many crop and flowering plants.4

As the dogwood seeds ripen in mid and late summer, we can watch the birds clear them from the branches and disperse the seeds to begin the dogwood life cycle anew. The dogwood and its predators require interaction with the soil microbiome and the vast ecosystem it supports. It is all a fragile system, which we should take care to respect and support.

References
1  https://www.nwf.org/nativeplantfinder
2  Wagner, David L. Caterpillars of Eastern North America. Princeton University Press, Princeton/Oxford. 2005.
3  https://breedingbutterflies.com
4. https://www.whatsthatbug.com

Book Review – Braiding Sweetgrass: Indigenous Wisdom, Scientific Knowledge, and the Teachings of Plants

— This review by Anne Raver first appeared in WildfloraRI, Spring 2019

Robin Law Kimmerer begins Braiding Sweetgrass with the story of Skywoman, who falls from a hole in the Skyworld, clutching a bundle of branches with many fruits and seeds. She hurtles downward, in a shaft of light, where there was only darkness before, toward the murky water below. Many eyes in the sea are watching, and geese rise up to break her fall, holding her in their soft feathers. A great turtle offers his back for her to step upon, a muskrat dives deep into the water to bring a handful of mud from the depths below. Skywoman spreads the mud on the turtle’s shell, scatters the seeds in her hand, and dances the world from brown to green.

Kimmerer, a botanist and member of the Citizens Potawatomi Nation, combines science and the knowledge of her indigenous ancestors to contemplate the devastation that we humans, particularly descendants of the first white settlers, have wrought since first setting foot in the so-called New World (which, as Kimmerer points out, was only new to Europeans and other immigrants; to native inhabitants, it was as ancient as the creation story).

Kimmerer is a distinguished professor at the SUNY College of Environmental Science and Forestry in Syracuse, NY, where she also founded and directs the Center for Native Peoples and the Environment. The center works with tribal partners and students to integrate traditional ecological knowledge with scientific research for restoration and sustainability projects.

Kimmerer also is a poet and a storyteller, and Braiding Sweetgrass weaves together many threads– stories of her childhood, of her own children, of her graduate students, of desecrated lands and healed ones—with the page-turning power of a beautifully written novel. At the same time, her mind, sharpened by both science and the observational skills of her tribal elders, is constantly analyzing the particulars of any given situation, be it the near extinction of wild salmon in the Northwest, or the chemical toxins that Allied Chemical poured into Onondaga Lake, or the day her daughter refuses to recite the Pledge of Allegiance in elementary school. (Kimmerer recalls her own childhood participation in the puzzling ritual, with its reference to God and the republic: “And you didn’t have to be an eight-year-old Indian to know that ‘liberty and justice for all’ was a questionable premise.”)

As a Potawatomi, Kimmerer considers plants and animals her teachers; she was listening to the trees long before scientists discovered how they communicate through pheromones in the air and mycorrhizae, a vast symbiosis of fungi and roots beneath the forest floor. Sweetgrass, or “wiingaashk, the sweet-smelling hair of Mother Earth,” was one of the plants that Skywoman clutched in her hand, the day she fell out of that hole in the sky. It was a gift, just like all the other plants, just like the land itself, to be passed from hand to hand shared but never sold. A metaphor for sharing and reciprocity, rather than taking from the earth and others, Sweetgrass calls for a radical shift in consciousness.

As a teacher and activist, Kimmerer offers many examples of people working together to restore balance to the earth—to bring back salmon to their spawning grounds, to restore polluted lakes and salt marshes, to simply learn to listen to the plants and animals.

Events

Recorded Virtual Lecture – Enhancing Delaware Highways: Lessons from the Roadside

Watch the recording on our Previously Recoded Programs/Events

On November 21, RIWPS invited Dr. Susan Barton from the University of Delaware Plant and Soil Science Department to give a virtual lecture focusing on  20-year project with the Delaware Department of Transportation that has provided many experiences with using native plants in stressful situations.  She discussed how the lessons learned in planting and editing roadsides can be applied to a variety of landscapes and illustrate strategies for managing landscapes sustainably and provide guidelines for promoting native plants and combating invasive plants in public and private spaces.

Landscapes. Highway, 50+ community landscape and private residence landscape

3 landscape projects – Delaware Highway, Private Residence, Fifty + Community

image of Sue Barton

Dr. Barton has worked closely for the past 20 years with DelDOT to research and implement new roadside vegetation management strategies.  She has also worked with partners to develop the Plants for a Livable Delaware Program, designed to provide alternatives to known invasive plants species and to promote sustainable landscaping.  She teaches Plants and Human Culture, Farm to Table, Field Sketching of Landscape Subjects, Landscape Architecture Symposium and coordinates the Landscape Horticulture Internship.  She also works closely with the nursery and landscape industry, writing newsletters, organizing short courses and conducting horticulture industry expos with the Delaware Nursery and Landscape Association.  Susan received the Nursery Extension Award in 1995 from the American Nursery and Landscape Association and the Ratledge Award for service from the University of Delaware in 2007. Susan received her SITES AP certification in summer 2017.  See her blog.

PDF of the Lecture

Additional Resources recommended by Dr. Barton