How to fight Insectageddon with a garden of native plants
March 23, 2018 by Nina M. Zitani, The Conversation
People across North America love to garden, yet the vast majority of garden plants are non-native species. Day-lilies, peonies, roses, chrysanthemums and butterfly bushes, just to name a few, are all non-natives. They evolved in far-away places such as Europe and Asia and people transported them to North America.
With Insectageddon —the great insect die-off —upon us, it's time to rethink our gardens.
Habitat destruction is the primary cause of the decline in biodiversity. Around the world, wildlife habitat has been destroyed by a variety of human activities such as residential and commercial development, agriculture and mining operations.
But gardeners can help to reverse the trend in biodiversity loss by creating backyard habitat, and native plants are the key.
Gardening with native plants has a long history in North America, but it remains under the radar of mainstream gardening. It's time we embraced our native plants and the biodiversity that comes with them.
Our feathered —and furry —friends will thank us for it.
And if you're an insect hater, now might be a good time to rethink that attitude
A giant swallowtail butterfly feeds from the flower of an alternate-leaved dogwood. Credit: Nina Zitani, Author provided
Many insects are picky eaters
The caterpillar of the giant swallowtail butterfly feeds on the leaves of hoptree. Credit: Nina Zitani
It was hot and steamy in the Costa Rican tropical forest. I was looking for caterpillars —the cute, wiggly, multi-legged and often furry larval stages of moths and butterflies.
As a graduate student at the University of Wyoming, I wasn't studying caterpillars per se, but looking for new insect species. My job was to search for parasitoid wasps —minute, non-stinging wasps that spend their immature stage living inside caterpillars.
I collected the caterpillars in plastic bags along with the fresh green leaves they were feeding on, and brought them back to the field station for rearing.
But before I knew it, I was headed back into the forest. The caterpillars were leaf-eating machines and needed fresh leaves often. But I couldn't just go into the forest and grab some leaves. I had to find the exact plant species the caterpillars were eating, or they would starve and die.
And that's how I learned that caterpillars, most of them anyway, are picky eaters.
Neatly tucked away in the scientific literature, you'll find the fascinating story of plant-animal co-evolution that began millions of years ago during the Mesozoic Era. There are many outcomes of that co-evolution, such as pollination, seed dispersal and the close relationship caterpillars (and other plant-feeders) have with their food plants.
Today, flowering plants produce toxic chemicals in their leaves to deter animals from eating them. But some animals, namely caterpillars, have adapted to eat the plant leaves —toxins and all.
So if you're interested in creating wildlife habitat in your backyard, then you're going to need the favourite food plants of insects. Insects will then thrive in your garden —as will the many larger animals that depend on insects for food.
The caterpillar of a monarch butterfly on a milkweed plant. Credit: Shutterstock
What is a native plant?
To better understand the concept of a native species, consider common milkweed and its relative, the dog-strangling vine.
Both are members of the milkweed family and found today in North America. Common milkweed is a native plant —it evolved in North America thousands of years ago, along with some other animals, including the monarch butterfly and the milkweed tussock moth. Today it is vital to the survival of those species.
But dog-strangling vine is a non-native plant from Europe that was introduced to North America by settlers in the 1800s. Monarch caterpillars and other native milkweed specialists that hatch on dog-strangling vine die because they can't eat it.
To make matters worse, dog-strangling vine has become an invasive species, forming dense colonies that displace native plants and their associated animals, contributing to biodiversity loss.
(No, it does not strangle dogs, by the way.)
Planting for the birds
Birds (and other larger animals) depend on bugs. "Nearly all terrestrial birds rear their young on insects, not seeds or berries," writes Doug Tallamy in his book Bringing Nature Home.
A caterpillar and a bumblebee on native Carolina rose. Credit: Nina Zitani
A simple way to think of it is this: Native plants maintain natural ecosystem food webs, whereas non-native plants don't. Native plants will attract and support healthy insect populations in your garden, which will provide essential food for birds and other animals.
There are thousands of native, or wild, North American pollinator species, including approximately 4,000 native bees and about 700 native butterflies, not to mention other pollinating insects such as moths, flies and beetles.
The leaves of native plants provide the food for caterpillars. The flowers of native plants provide food —pollen and nectar —for the pollinators.
When we consider the entire life cycle of insects, the essential role of native plants becomes clear.
And let's not forget the non-native honey bee, one of the few domesticated insect species. Although the honey bee is not wildlife, it does pollinate some crops and produces honey. It too will find plenty of food in a native plant garden.
Small gardens, big impact
My family kicked off our native garden by planting a single common milkweed plant into our tiny urban garden. The following summer it bloomed, and when a monarch butterfly landed on it, we were hooked.
When we moved to a larger property years later, we decided to create a monumental garden full of biodiversity.
A simple way to think of it is this: Native plants maintain natural ecosystem food webs, whereas non-native plants don't. Native plants will attract and support healthy insect populations in your garden, which will provide essential food for birds and other animals.
There are thousands of native, or wild, North American pollinator species, including approximately 4,000 native bees and about 700 native butterflies, not to mention other pollinating insects such as moths, flies and beetles.
The leaves of native plants provide the food for caterpillars. The flowers of native plants provide food —pollen and nectar —for the pollinators.
When we consider the entire life cycle of insects, the essential role of native plants becomes clear.
And let's not forget the non-native honey bee, one of the few domesticated insect species. Although the honey bee is not wildlife, it does pollinate some crops and produces honey. It too will find plenty of food in a native plant garden.
Small gardens, big impact
My family kicked off our native garden by planting a single common milkweed plant into our tiny urban garden. The following summer it bloomed, and when a monarch butterfly landed on it, we were hooked.
When we moved to a larger property years later, we decided to create a monumental garden full of biodiversity.
A monarch butterfly gathers nectar on a native daisy commonly called cup plant. Credit: Nina Zitani
We travelled for hours to purchase plants from nurseries that specialized in locally sourced native plants. Over several years, we planted more than 100 native species, including two kinds of milkweed, nannyberry, daisies of all sorts, multiple kinds of roses, dogwoods, elderberry and more.
We also planted hoptree (Ptelea trifoliata, a Citrus relative), the food plant for the caterpillar of the giant swallowtail, North America's largest butterfly.
You don't need to have a huge garden to support wildlife. Start small, and plant just one native plant. Butterfly milkweed is a great choice, but there are thousands of native species to choose from. Starting small is better than not starting at all.
It's easy to get started. The Nature Conservancy of Canada publishes the "Native Gardening 101" guide. The USDA Plants Database has species range maps for all of North America and allows you to search on common names of plants such as butterfly milkweed. The Ontario Invasive Plant Council's "Grow Me Instead" guide includes many native plant options.
Nature Needs Half is a growing conservation movement. A reasonable end goal might be to devote half of your garden to native plants.
A year after we planted the hoptree, we spotted a giant swallowtail butterfly laying eggs on its leaves. Several days later we found the caterpillars eating the leaves, and we celebrated.
But not for long —we had gardening to do!
Explore further: Butterfly gardens offer some hope for pollinators
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Native Plants Support the Local Food Chain
For those hoping to support local insect species, Wagner says the place to start is at the bottom of the food chain, by ensuring that there is a wide variety of native plants available as food for insects and other wildlife.
A sparrow feeds a caterpillar to its young. A mother bird needs hundreds of caterpillars to raise a clutch of nestlings. Credit: Doug Tallamy
Connecticut ecology and evolutionary biology professor David Wagner, points out an important but often overlooked concept, that ornamental and exotic plants rarely support the local food chain like native plants do. Native insects and native plants evolved together, and over time, developed intimate associations and adaptations for one another.
Planting exotic species limits the potential of yards and parks to support wildlife. And non-native plants become doubly problematic if they are invasive. Many forests in the Northeast are becoming dense thickets of Oriental bittersweet, multiflora rose, Japanese barberry, and winged burning bush, plants that are able to thrive in part because many native animals cannot or will not eat them.
"Invasive plants usually don't have close associations with native species," Wagner says. "Among the biggest losers are herbivorous insects that are dietary specialists – their fates are inextricably bound to those of their host plants. As native plants are overrun by barberry and bittersweet, so will go Connecticut's specialized bees, butterflies, and other natives. In habitats overrun with invasive plants, we often get more 'weedy' species higher up the food chain: robins, starlings, English house sparrows, while losing the buntings, warblers, and more specialized birds.
A smorgasbord of plants will support a healthy mix of insects that in turn will support a healthy mix of songbirds and other animals all the way up the food chain. To make a songbird, you have to have caterpillars – to raise a clutch of nestlings, a mother bird will need hundreds. Plant exotic ornamentals that don't attract local insects and you might as well hang a sign that reads, "Songbirds not welcome."
"We need to be more mindful about the decisions we make, one tree at a time, one yard at a time, one campus at a time," says Wagner. "We need to plant things that will support local biodiversity."
Wagner encourages homeowners to explore their own backyard biodiversity, as he did when he first moved to Connecticut, by going out into the yard by day, by night, exploring by flashlight, or simply by shining a light on a sheet to attract insects, and of course take pictures or make notes on what is observed.
"There's so much going on in one's backyard in Connecticut," says Wagner. "It's a mini-jungle of sorts, rife with creatures." Let's keep it that way. Instead of a gingko, plant a white oak, native cherry, or highbush blueberry.
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