Text and photos by David George reporting for Native Plant News
Think moths are just drab little creatures that flutter around your porch light? Actually they are incredibly diverse and ecologically important, with over 3,000 species of moths in North Carolina compared to just 177 butterflies. And they are closely tied to our native plants, more than a thousand of which serve as hosts for moth caterpillars.
In 1962, Rachel Carson warned of a “spring without voices,” painting a grim picture of a rapidly approaching morning where “only silence lay over the fields and woods and marsh.” Though we have made a great deal of progress since the publication of Silent Spring, more than 60 years later we again find ourselves at the precipice of ecological catastrophe. Entomologist David Wagner and others have warned of an “insect apocalypse” which could result in the same silent spring morning. Study after study from around the world have revealed insect populations in collapse, declining perhaps ten percent per decade. Surveys by the North Carolina Biodiversity Project suggest that moths and other insects are rapidly declining in abundance and diversity in our own state.
While the conservation movement has traditionally focused on plants, birds, and other large “charismatic” animals, in recent years there has been increasing attention to the importance of insects. As primary producers, plants are clearly the base of our varied ecosystems, but it is insect herbivores that convert this plant biomass into a form that is accessible to the rest of the food web. And in many terrestrial ecosystems, it is moth caterpillars that are the primary herbivores. Songbirds are completely dependent on caterpillars to feed their nestlings. Staggering numbers of caterpillars are required. In The Living Landscape, Doug Tallamy estimated that it might take up to 10,000 caterpillars to rear a single nest of Carolina Chickadees! And many other animals are dependent on caterpillars and other insects for food, not to mention the important role that moths and butterflies play in pollination.
I hardly need to convince you of the importance of native plants, but let me make the case from an entomological perspective. Moths and other insects have co-evolved over millions of years with native plants. In this evolutionary arms race, plants have come up with ever more effective chemical and physical defenses, while their insect herbivores have found ways to circumvent these defenses. This has resulted in a high degree of specialization and most of our native moths are food plant specialists, eating only plants within a particular family or genus. Non-native plants support relatively few moth species. I have never seen a caterpillar on a Crape Myrtle or a Bradford Pear. And not all natives are equal when it comes to supporting moths. A summary of the top host plants in North Carolina can be found on the NC Biodiversity Project website.
While some plants are better than others from a moth perspective, the key is planting a wide range of native plants to support the greatest number of moths and other insects. As Tallamy writes in The Living Landscape, “What type of landscape is capable of producing insects in the numbers required to support viable food webs? A landscape built from a diversity of plants that have each developed specialized relationships with a diversity of insect species.”
The best hosts are also some of our most common plants–trees like oaks, hickories, maples, cherries, elms, and willows. Among herbaceous plants, goldenrods, asters, coneflowers, and evening-primroses are all productive hosts. Many of these are plants you probably already have in your yard, and the others you should be able to find easily at local nurseries. Other good native plants are not particularly good hosts–Beautyberry and Mountain Laurel, for example, support relatively few caterpillar species. This is not to say that you shouldn’t plant these species.
So why are our moths and other insects in such trouble? There is no simple answer, with many factors contributing – what David Wagner has referred to as “death by a thousand cuts.” Perhaps the biggest issue is habitat loss, along with the associated loss of native host plants. Not only are we continuing to cut down forests for new developments, we are replacing native plants with ornamental species that support very few insects. A walk through the typical suburban development shows a landscape dominated by turf grass and non-native trees and shrubs. While it may appear green, from an insect perspective it is a desert. Among the other factors contributing to the decline of insects are climate change, light pollution, and the indiscriminate use of pesticides. All of these problems need to be addressed, but we also need a fundamental shift in public sentiment from seeing insects as something to be eliminated to seeing them as a vital part of the ecosystems upon which we all depend.
Part of the work of the North Carolina Biodiversity Project is to publish a collection of websites cataloging the diversity of life found within our state. The Vascular Plants of North Carolina is a great reference for finding native plants suited to your area. The site lists all of the plants found in our state, and the plant list can be filtered just to show the roughly 2,900 native species. A good deal of my work in recent years for the Moths of North Carolina website has been to investigate moth host plant relationships, and I have been gradually building a host plant database from the literature, field work, and submissions to our site. So far we have confirmed over 1,000 host plants, though this covers only about a quarter of the 3,000+ moth species in North Carolina. The database can be accessed from the Larval Hosts tab of the Moths of NC homepage. Selecting a plant genus will provide you with a list of all the moth species that potentially feed on that genus, and show which plants have been confirmed as hosts.
We need your help with our research – please submit records of caterpillars on native plants to our website, or send them directly to me at ncbiodiversityproject@gmail.com if you don’t know what kind of caterpillar it is. And keep up the good work championing the importance of native plants!
David George is a science educator and naturalist based in Durham. In addition to his work at the Museum of Life and Science, he is the head of education and outreach for the North Carolina Biodiversity Project. David is co-author of the Moths of North Carolina website, and travels around the state sampling moth populations and investigating host plant relationships.