Butterflies are one of the showiest and most beautiful insects that visit our gardens. However, they are more than just a pretty “face.” They are also important plant pollinators and indicators of environmental health.
Insect pollinators are necessary to the healthy reproduction of over 80% of the world’s flowering plant species (Edward S. Ross). However, pesticide use, the loss and fragmentation of habitat and the degradation of remaining habitat have caused dramatic declines in many insect populations worldwide. In the San Francisco Bay area alone, four endemic butterfly species are already extinct and seven others are endangered (The Alameda Butterfly Habitat, 2004).
Pollinators are keystone species. This means they are species on which the existence of a large number of other species depends. Pollinators are essential to the reproductive cycles of most flowering plants and thus to the ecosystem itself, supporting plant populations that other animals and birds rely on for food and shelter. As the butterflies and other insects on which many native plants depend for adequate pollination disappear, the effect on the health and viability of these native plant populations can be disastrous.
What can we do to slow, or even prevent, the further decline in pollinator and butterfly populations?
Slowing the relentless destruction of habitat and reducing the use of pesticides are important goals in conserving pollinator populations. However, there are also easier and much more readily achievable steps we can take immediately in our own lives and back yards:
- Include plants in our yards that provide food and habitat for wildlife.
- Stop using pesticides in our yards.
- Combat fragmentation of habitat by encouraging neighbors to adopt wildlife-friendly gardening and planting practices, thus providing “corridors” of habitat.
- Buy organic food and household products whenever possible.
Providing Habitat for Butterflies
Butterflies’ needs are relatively simple:
- A warm, sunny location sheltered from strong winds.
- Sites for perching, resting and sunning so that they can warm their wings for flight. A large rock or log in a sunny spot is perfect.
- A large number of appropriate, sweet-scented, nectar-producing, colorful flowers that provide a progression of blooms from spring through late fall.
- Appropriate host plants on which the butterflies can lay their eggs.
- A supply of water.
- An environment free of pesticides and herbicides.
- Safe places in which to form a chrysalis.
A butterfly garden should contain plants that attract the butterfly species most common in your area. Unless you live very close to a natural area that contains the appropriate host plants, you should grow the plants that provide food and and habitat for all stages of the life cycle of your local butterflies i.e. egg, larva (caterpillar), pupa and adult. In this way, your garden should attract and support complete butterfly populations.
If you care about butterflies and other beneficial insects and want to attract them to your garden, remember to avoid using insecticides, including organic products such as Bt (Bacillus thuringiensis) which kills caterpillars. A chemical-free environment will also benefit birds and other wildlife by providing more insects for them to eat.
In addition to nectar, adult butterflies also need a source of water and salts. Unlike birds, butterflies will not drink from open water, preferring to drink from a patch of wet mud, although some like tree sap or overripe fruit.
Remember to prune shrubs and perennials carefully so that you can keep and eye out for hidden chrysalides.
Adult butterflies rely on nectar for their daily fuel that they “drink” from nectar-producing flowers. When planning your butterfly garden plant list, consider the flowering time of each nectar-providing plant and aim to provide a continuous succession of blooming from spring through fall. A list of recommended nectar plants that do well in the Monterey Bay is given in Table 1.
Different butterfly species have different flower color and shape preferences. Pink, red, orange, and purple are considered the most attractive adult nectar source colors, but they also use yellow, blue and white flowers.
The anatomy of many butterfly species’ feeding structures is effective only on specific flowers, so make sure you are planting plants that attract the type of butterflies you want in your garden. The shape of a flower determines which butterfly species can gather its nectar. The length of the butterfly’s tongue and the flower tube must be similar for the butterfly to reach the nectar at the base of the tube.
Most butterflies prefer nectar plants whose “flowers” are actually compact heads made up of tiny individual florets, giving the butterfly multiple rewards for each stop. This butterfly-attracting strategy is used by many kinds of plants, including all members of the aster (Asteraceae), carrot (Apiaceae), knotweed (Polygonaceae) and verbena (Verbenaceae) families plus many others.
(Please see table 1 below.)
Larval Host Plants
The larvae (caterpillars) can be much more selective than the adults when choosing host plants for their food and shelter, feeding only on certain plants to which their species is adapted. M ost butterfly species are limited to a single plant family and, sometimes, to a single genus.
Many of the larval host plants are not what we would normally consider gardenworthy or ornamental. Indeed, many people would consider them weeds and, consequently, they are not often planted. As a result, many gardens attract only the larger, wide-ranging butterfly species.
If you want to attract some of the smaller, stay-at-home species of butterfly, you might try growing their favorite larval hosts as well as nectar plants. Or, if your garden is close to a wild area with plants that support the larval stage, you could plant just the nectar plants in order to attract adult butterflies to your garden.
The larval plants preferred by butterflies in the Monterey Bay area are listed in Table 2.
(Please see table 2 below.)
Butterflies in the Monterey Bay Area
There are about ninety species of butterflies in the Monterey Bay area. However, many of these are locally rare or only occur in mountain, forest or chaparral environments. The fifty species that are most likely to occur, or become established, in the Monterey Bay area are listed in Table 2 together with their preferred larval food plants. Of these fifty, only twenty are likely to be seen with any regularity.
Members of 45 plant families have been documented as larval foods for the 90 local butterfly species. However, only 22 of these plant families are essential or of major importance to one or more butterfly species. The other 23 families are alternate foods of minor importance.
The plant families on which the largest number of local butterfly species depend for larval food are the Poaceae (13 species), Fabaceae (12 species), Malvaceae (7 species.), Brassicaceae (6 species), Rhamnaceae (6 species), Asteraceae (5 species), Salicaceae (5 species), and Fagaceae (5 species).
In the following list, the 20 butterfly species that are in bold, italicized type are those most likely to be present in the Elkhorn Slough area. Plant names in bold type are the most worthwhile growing in this area to enhance larval supply.
(Please see table 2 below.)
References and Further Reading
- Ellis BW, Bradley H Atthowe and Yepsen R, 1996, The Organic Gardener’s Handbook of Natural Insect and Disease Control, Rodale Press, Emmaus PA.
- Emmel TC, 1997, Butterfly Gardening: Creating a Butterfly Haven in Your Garden, Friedman/Fairfax Publishers, New York
- Jackson B and Baines V, 1999, Mindful of Butterflies, The Book Guild, Lewes UK.Pesticide Action Network, 2000, Hooked on Poison: Pesticide use in California 1991-1998, Pesticide Action Network North America, San Francisco (also available on-line at www.panna.rg/resources/documents/hookedAvail.dv.html)
- Pyle RM, 1992, Handbook for Butterfly Watchers, Houghton Mifflin, New York.
- Scott JA, 1986, The Butterflies of North America: A Natural History and Field Guide, Standford University Press, Stanford.
- Shepherd M, Buchmann SL, Vaughan M and Hoffman Black S, 2003, Pollinator Conservation Handbook, The Xerces Society, Portland Oregon.
- Xerces Society and Smithsonian Institution, 1998, Butterfly Gardening: Creating Summer Magic in Your Garden, Sierra Club Books, San Francisco.