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Tucson Audubon Society Reprinted from the July-August, 2001 Vermilion Flycatcher, newsletter of the Tucson Audubon Society. Urbanization
and Butterfly Populations Because of the extraordinary diversity of its habitats and proximity to Mexico, Southeast Arizona is rich in butterfly species. The loss of riparian areas and pristine desert to development has taken its toll on native butterfly populations. However, the planting of larval foodplants and nectar plants, as well as avoidance of harmful practices, may help create urban habitats. As an amateur butterfly gardener living in Tucson for the last four years, I would like to share some of my discoveries. Butterflies are often observed nectaring at flowers. Although not all butterflies require nectar, they all need their larval foodplant; that is, the plant the caterpillar eats before it forms a chrysalis. Many of these hardy native shrubs and trees are cleared away with encroaching civilization. And while many nectar plants are sold at nurseries, some foodplants are not always available. Desert Hackberry (Celtis pallida), for example, the host plant for the American Snout and Empress Leilia, is not easy to find for sale. Saltbush (Atriplex canescens) is amazingly drought tolerant and is a wonderful choice for the arid zone of the garden. The foodplant for what may be the world’s smallest butterfly, the Pygmy Blue, Saltbush is not often promoted by nurserymen. Yet this large shrub would be an excellent performer in a school butterfly garden: it requires little or no supplemental water after the first year, and no pruning...and in September it comes alive with dozens of tiny coppery-winged Pygmy Blues. It is surprising that even native plant nurseries continue to heavily feature Australian Sennas (also known as Cassias) rather than our native Sennas, such as Senna covesii, Senna leptocarpa, and Senna wislizenii. Native sennas serve as foodplants for Cloudless Sulphurs and Sleepy Oranges. The Australian species, on the other hand, are usually poisonous to the young caterpillars. (I have been informed, however, of one instance in which caterpillars did develop while eating an Australian Senna.) Although native Sennas are dormant in the wintertime, they are covered with beautiful yellow blooms from summer to fall. As an added bonus, they also attract those great pollinators, Carpenter Bees. So a small step such as choosing a native over an exotic can have an impact on butterfly populations, as well as providing food for other insects. The host plant of the Phaon Crescent, Frogfruit (Phyla nodiflora or Lippia nodiflora), was once common in Tucson. While no records exist from collected specimens, the Phaon Crescent may have once been a frequent garden visitor in this area. The Southeast Arizona Butterfly Association has organized the Frogfruit Project to encourage butterfly enthusiasts to cultivate this native groundcover in the hope of establishing the Phaon Crescent in Tucson. For more information, visit the SEABA website at: www.naba.org/chapters/nabasa/home.html. Caterpillars will also lure birds to your garden! Last summer, Aberts Towhees, Mockingbirds, Thrashers, and Cactus Wrens feasted on Cloudless Sulphur caterpillars that were feeding on Sennas. Migrating orioles also like to devour caterpillars. Providing plants for butterflies can aid in sustaining migrating as well as our urban birds. The use of pesticides to control caterpillars is strongly discouraged—unwanted caterpillars can be picked off if necessary. Gardening practices can also play a role in increasing butterfly survival. In urban areas, weeds are considered unsightly and are therefore usually quickly removed. Many butterflies, however, lay their eggs on these weeds. Sara and Pima Orangetips, for example, eat plants from the mustard family; Checkered Skippers prefer mallows; Red Admirals munch on nettles. While not all weeds should be left because they could constitute a fire hazard, maybe some controlled weedy areas could be allowed in both public parks and private gardens. The other day, I noticed a Dainty Sulphur ovipositing on Golden Dyssodia (Shrubby Dogweed) in the common area of my neighborhood. I knew that these eggs would never hatch because the gardener would arrive shortly to pull out this native wildflower. Thanks to the winter rains, an unusual number of these ground-hugging plants were sprouting everywhere. They could not all remain, but surely some could be left to support the Dainty Sulphurs. Pipevine (Aristolochia watsonii) is another weed that fills a niche in urban neighborhoods. If people knew how to identify it, then it may have a chance to grow into a huge cluster under a tree where it could provide food for the caterpillars of the striking Pipevine Swallowtail. Because Pipevines have small leaves, they are often unable to supply enough food for even a single caterpillar, so the larva must attempt to locate another Pipevine nearby. Planting this native vine may help increase the numbers of this gorgeous Swallowtail. In the wild, dead flower stalks and leaf litter simply remain in place; in urban gardens, they are often cut off and cleared away. This plant material may harbor caterpillars or their chrysalises. The Great Purple Hairstreak, for example, pupates under leaf litter under the bases of trees. Some caterpillars require or prefer wilted flowers and seedheads to complete their development once the growing season begins. While it is not feasible (or desirable) to let all plant litter remain, a completely tidy garden is less valuable to butterflies than one with some amount of brown stalks, seeds, and dead leaves. A final aspect of urban life that should be considered is the growing trend of releasing butterflies at weddings. This unfortunate custom poses a threat to native butterflies. Commercially-raised butterflies may spread diseases and epidemics to native butterfly populations. They may also affect the genes of native butterflies: a recent report (Moore, P.D. 2000, “Conservation biology: Seeds of Doubt,” Nature 407: 683-685) suggests that the fitness of local butterfly populations may be decreased by interbreeding with released individuals, by the introduction of genes that are not optimal for the local environmental conditions. In addition, scientific studies of migration are confounded by butterfly releases. Scientists trying to track, for example, northward movement in the spring of Painted Ladies are now confused by Painted Ladies being released in the environment. Let’s help spread the word to discourage this practice! In the words of Jeffrey Glassberg, president of the North American Butterfly Association, et al., “There’s no need to release butterflies; they’re already free”! Bibliography Brock, Jim, Lifestyles of the Scaled and Beautiful: Great Purple Hairstreak, American Butterflies, vol. 7:1 (Spring 1999), p. 39-41. Glassberg, Jeffrey, Butterfly Releases: Action You Can Take, American Butterflies, vol. 8:4 (Winter 2000), p. 2 and 47. Glassberg, Jeffrey, Opler, Paul, Pyle, Robert M., Robbins, Robert, and Tuttle, James, There’s No Need to Release Butterflies, They’re already Free, American Butterflies, vol. 6:1 (Spring 1998), p. 2. Swengle, Ann, Garden Cleanup, Butterfly Garden News, vol. 4:3 (Fall 1999), p. 1; 4-6. Editor’s Note: This article is the fourth in a series on the effects of urbanization upon wildlife. Bird questions? Check Birding | General questions? Contact: Tucson Audubon Society | Webmaster: Email This page was updated on 02/09/06 |