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If we continue to kill off leaf-eating insects, larger animals will die out too.
Bugs in the Garden : Why We Need Them
April 8, 2009 by Evelyn J. Hadden

Douglas Tallamy spoke for two hours about bugs, and his rapt audience wanted more. They lined up to ask questions, thank him, and buy his book, Bringing Nature Home.

Tallamy's two-pronged message centers on our antagonistic relationship toward bugs and our preference for exotic (non-native) plants in our landscapes. In his talk and his book, he presents a series of shocking research results and statistics, tied together into a flashing neon arrow that points to humble gardeners (and their urban and suburban landscapes) as the saviors of our planet.

Here are the main steps in his logic:

  1. Humans have taken possession of 95% of the land area in the US (41% is agricultural, 54% is metropolitan areas including suburbs, and 5% is "wilderness").

  2. We have tried to reduce insect populations by breeding and favoring "pest-free" plants (both ornamental and edible), and by spraying insecticides and using bug zappers. A more sustainable approach would be to plant diversely and allow populations of many different bugs and bug predators to reach a balance, and this would ensure only minimal (and hardly noticeable) damage to our plants.

  3. Plants convert sunlight and carbon dioxide from the air into simple sugars and carbohydrates, forming the essential base of the food chain. Without plants, all animals (including humans) would die. But plants defend themselves against plant-eaters with chemicals that are toxic, taste bad, and/or retard digestion.

  4. Leaf-eating insects transfer energy from the plants to higher-order animals. They supply protein and fat bodies that are a key part of the diet of smaller animals, who in turn make up the diet of larger animals. When leaf-eating insect populations are reduced, so are the populations of the birds and animals who depend on them for food. Notably, leaf-eating insects are the main food source that 96% of our terrestrial birds feed their young. ("We feed birds all winter long," said Tallamy, "then in Spring when they try to make more birds, we starve them.")

  5. Leaf-eating insects, with rare exceptions, eat only the leaves of a few plant species with which they have co-evolved (and thus whose chemical defenses they have developed ways to overcome). A well-publicized example is the monarch butterfly and milkweeds, which are the only source of food for monarch caterpillars.

  6. Our fragmented system of parks does not include enough or large enough tracts of land to sustain our biodiversity of native plants and animals. Unless we plant more native plants (insect food) in our home landscapes, most of our native animals are headed toward extinction. According to Tallamy's research, caterpillar biomass (baby bird and animal food) is 35 times greater on native plants than on non-natives; on average, alien woody plants support 4 insect species while natives support 72 species. This means that native woody plants produce 35 times more baby bird biomass.

Given the grim scenario he paints, Tallamy is able to follow up with a surprisingly hopeful message, because there are definite steps each of us can take to change our collective course.

First, we must plant natives, especially trees and shrubs. As a bonus, these woody plants act as carbon sinks, removing large amounts of carbon from the atmosphere to build their tissues and thus mitigating climate change. (On pg 117, Tallamy writes that, according to a paper in the 2006 issue of Science: "climatologists are now unanimous" in their belief that atmospheric carbon dioxide raises the earth's surface temperature, that there is now more atmospheric carbon dioxide than at any time in the past 10 million years, and that human consumption of fossil fuels has caused this high level of atmospheric carbon dioxide. In other words, it now a scientifically accepted statement that climate change is happening and humans have caused it.)

Top native woody species to plant? Quercus (oaks), Prunus (cherries), Salix (willows), Betula (birches), Populus (poplars and aspens), Malus (apples), Acer (maples), Vaccinium (blueberries), and Alnus (alders).

Don't forget to add larval plants—food for the leaf-eating caterpillars—in addition to nectar plants to feed the butterflies they become.

Make corridors of denser plantings when possible, make them as wide as possible, and connect them to wilder areas and water bodies when possible. We can do this by making our lawns into clearings that are surrounded by denser plantings. "The biggest difference [you can make] is going to come from the amount of lawn you can transition to native plants," said Tallamy. In his book he adds another reason to shrink your lawn: "...reducing the amount of lawn you mow each week is one of the best things you can do to reduce your family's carbon dioxide emissions. On average, mowing your lawn for one hour produces as much pollution as driving 650 miles." - pgs 117-118

We must overcome our need for savanna-like surroundings and instead plant in vertical layers, including the eye-level shrubs that are crucial nesting sites for many birds. "Remember, it is the shrub layer rather than the tree canopy that birds most often use as nesting sites." - p.119

Stop mowing under your trees and instead keep the fallen leaves there. This improves tree health and creates habitat for insects and spiders (bird food). You can grow ferns and other woodland groundcovers to cover up the leaves.

Tallamy's parting words to his audience are memorable and inspire action. He said, "The way we landscape today is truly going to determine what life looks like tomorrow."

Tallamy just released the paperback version! Check it out :

Bringing Nature Home

Related info at LessLawn: Banning Lawn Pesticides (a review of the documentary A Chemical Reaction)

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