The Loma Prietan - March/April 2011

Gardening Green

In Defense of Insects

by Arvind Kumar

Native bee on lupine flower. Photo: Stephen Rosenthal
Native bee on lupine flower. Photo: Stephen Rosenthal

When we think of creating habitat, we are often motivated by glamorous species like birds and butterflies. We rarely think of attracting insects to our gardens because we associate insects with problems and pestilence.

Why are insects important? Pound for pound, the total insect population of the world weighs about six times as much as the human population; the earth really belongs to them. After plants, insects are the most important part of the food chain. Without them, many higher forms of life would cease to exist. Many birds, amphibians, and bats feed on insects. Insects help with pollination and decomposition of organic matter. When an ecosystem is in balance, insect populations are stable, one species keeping the other in check.

An insectary is a laboratory for the study of insects, a place where they live and breed and are observed. As an environmentally aware gardener, you can turn the garden into your own private insectary using insect-friendly native plants.

How do native plants help? The experimental evidence cited in Douglas Tallamy’s book Bringing Nature Home: How You Can Sustain Wildlife With Native Plants is dramatic and convincing. The data shows that insects overwhelmingly prefer native plants to non-natives:

  • Native plants produce over four times more insect biomass than non-native plants
  • Native plants attract more than three times as many species of insects as non-native plants
  • Native plants support 35 times more caterpillar biomass than non-native plants
  • Even among "generalist" insects (insects that consume both native and non-native plants), native plants produce twice the insect biomass than non-natives

In recognition of the special role of native plants in the environment, the state legislature has declared the third week of April to be California Native Plant Week. Celebrate it by introducing native plants to your garden - plant them, and the insects will come!

Here is a short list of my favorite insect-friendly native plants:

For spring, try sun-loving native wildflowers and perennials like Yarrow (Achillea millefolium), Arroyo Lupine (Lupinus succulentus), California Poppy (Eschscholzia californica), Globe Gilia (Gilia capitata), and Elegant Clarkia (Clarkia unguiculata). They are more effective when grown in masses or clusters.

California is home to many species of Wild Lilac(Ceanothus sp), which flower in a range of colors from blue to purple to white. They are pollen and nectar heaven for many kinds of bees and insects. Most are sun loving and easy to grow.

The white flowers of Holly-leaved Cherry (Prunus ilicifolia) are real magnets for insects of all kinds. This versatile plant is California’s answer to privet: it can be grown as a tree or pruned as a hedge. It is slow growing and drought tolerant. It looks neat and tidy the year round.

The fragrant candles of California Buckeye (Aesculus californica) flowers attract many butterflies in spring. The lime green foliage turns brick red by July and drops by August, revealing a graceful silver branching structure for the rest of the year.

Nothing beats the drawing power of California Buckwheat (Eriogonum fasciculatum) when it bursts into bloom with nectar-rich white flowers at the start of summer. This subshrub loves sunny slopes, and resents summer water. Cut it down to 6 inches each winter to renew.

Narrow-leaved Milkweed (Asclepias fascicularis) is a host and nectar plant for butterflies, but it also attracts a wide variety of insects and beetles, including colonies of aphids, which in turn attract ladybugs. Cut it to the ground in winter when it goes dormant.

Several varieties of Gumplant (Grindelia sp) are irresistible to butterflies and other insects. I am particularly fond of Coastal Gumplant (Grindelia stricta venulosa), a groundcover variety, and Valley Gumplant (Grindelia camporum), an upright perennial.

California Aster (Aster chilensis) blooms in summer and draws many insects. It appreciates sun and some summer moisture. Cut it to the ground in winter to rejuvenate for the next season.

Finally, no shrub supports insect life as well as Coyote Bush (Baccharis pilularis). The plant comes in upright shrubby forms and groundcover forms. Plant in full sun, and avoid summer water. Prune dead growth every 3-4 years to renew.

To create insect habitat, eschew pesticides and herbicides and use natural, organic alternatives. Be willing to tolerate minor plant damage; a plant that isn’t being munched is not doing its job in the environment! Teach your family members to replace their fear of insects with keen observation and a sense of wonder about the natural world.

Sierra Club life member and California Native Plant Society director Arvind Kumar grows native plants in his Evergreen garden. He can be reached at chhaprahiya@yahoo.com.