Historic, Archive Document Do not assume content reflects current scientific knowledge, policies, or practices. Jational Center of Forest s®7,62 realth Management Technology ■r\ Transfer Eastern Forest Caterpillars Common Caterpillars of Eastern Deciduous Forests David L. Wagner, Julie J. Henry, John W. Peacock, Michael L. McManus, and Richard C. Reardon United States Forest Service FHM-NC-04-95 Department of June 1995 Agriculture Acknowledgments Jane Carter helped with recordkeeping and provided much of the initial stimulus for this publication. Linda Butler, Tim McCabe, John Rawlins, and Dale Schweitzer identified caterpillars and David Smith determined the sawfly. John Rawlins, Daniel Kucera, Tim McCabe, and Rebecca Nisley made many helpful suggestions on drafts of the manuscript. The photograph of Anisota virginiensis was kindly pro¬ vided by James Tuttle. Steve Talley and Laura Neale supervised crews that collected many of the caterpillars photographed in this study. Others who generously sup¬ plied "livestock" include Robert Acciavatti (Ennomos subsignaria), Jeff Boettner (Papilio troilus), George Leslie (Nymphalis antiopa), John Natale (Eacles imperialis), Nathan Schiff (Schizura concinna), Dale Schweitzer (Asterocampa clyton and Hemileuca maia), and Ben Williams (Ceratomia undulosa). Valerie Giles collected and photographed many of the individuals figured here. Research leading to this publication was supported by USDA Forest Service Coop¬ erative Agreement 23-711, USDA Forest Service Gypsy Moth R & D Program and NSF grant BSR-9007671 given to DLW. Additional support came from the USDA Forest Service's National Center of Forest Health Management, Morgantown, West Virginia, and the Northeastern Center for Forest Health Research, Hamden, Connecticut. The policy of the United States Department of Agriculture (USDA) prohibits discrimination in its programs on the basis of race, color, national origin, age, religion, sex, or disability, political beliefs and marital or familial status. (Not all prohib¬ ited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact the USDA Office of Communication at (202) 720-5881 (voice) or (202) 720-7808 (TDD). To file a complaint, write the Secretary of Agriculture, U.S. Department of Agriculture, Washington, DC, 20250, or call (202) 720-7327 (voice) or (202) 720-1127 (TDD). USDA is an equal opportunity employer. Common Caterpillars of Eastern Deciduous Forests David L. Wagner and Julie J. Henry Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs John W. Peacock and Michael L. McManus USDA Forest Service, Northeastern Forest Experiment Station, Northeastern Center for Forest Health Research, Hamden, Connecticut Richard C. Reardon USDA Forest Service, National Center of Forest Health Management, Morgantown, West Virginia Although the caterpillar (or larva) of Lepidoptera (moths and but¬ terflies) is the life stage that is most commonly observed feeding upon or defoliating trees and plants, there are relatively few pub¬ lished sources available that can assist in the identification of even the most-common species. This is all the more surprising because caterpillars are often more conspicuous, sometimes more easily identified, and always more abundant than the moth or butterfly (adult) stage. This pamphlet was prepared to facilitate identifica¬ tion of common caterpillars encountered in eastern deciduous hardwood forests and to foster a greater appreciation for the diver¬ sity in color and form that is found in caterpillars. The hardwood forests of the eastern United States are home to more than 2,000 species of Lepidoptera, perhaps a third of which have caterpillars that feed externally on foliage. Yet only a minute fraction of this rich fauna is commonly seen. The vast majority of lepidopterous larvae are either too secretive in habit or occur in such low numbers that they are rarely encountered. We have selected known pest or outbreak species that often co¬ occur with the gypsy moth in mixed forests. Other species such as silkworms, butterflies, and those with conspicuous caterpillars such as the woolly bear are included because they are often the subject of public inquiry. For each species, we provide both a common and scientific name. Where different common names exist for the caterpillar and adult of the same insect, we use the name that is applied to the caterpil¬ lar. For example, the caterpillar of Dryocampa rubicunda is called the 1 green-striped mapleworm, but the species is perhaps more familiar to many entomologists as the rosy maple moth. Brief descriptions mention diagnostic characters and other similar appearing species. The most frequently used terms helpful in identification are pro¬ vided in figure 1. For a few groups, it may be necessary to exam¬ ine the crochets (hooklets) on the fleshy prolegs (figures 2 and 3). Consult the glossary (page 28) for unfamiliar terms. Few serious color field guides to caterpillars have been attempted. This publi¬ cation hopes to fill that gap for an audience that would include many entomologists, foresters, naturalists, interpretive specialists, extension agents, and hobbyists. mnttm imn Figure 1—Diagrammatic sketch of a caterpillar. Figure 2—Arrangement of crochets (hooklets) on midabdominal proleg of a noctuid. Figure 3—Arrangement of crochets (hooklets) on midabdominal proleg of an arctiid. Host Plants Although caterpillars may feed on a single plant genus or species (monophagy), many species associated with hardwood forests feed upon a wide array of trees and shrubs (polyphagy). For polypha- gous species, we list examples of favored host genera. Ffost prefer¬ ences frequently vary over the range of an insect—a species that in one area appears to be a specialist, using only one or two closely related plant genera, may feed on a wide array of plants across its geographical range. Although host association data may occasion¬ ally aid the identification of larvae, you will likely find caterpillars occurring on hosts that are not listed here. Moreover, many cater¬ pillars wander over plants on which they do not feed, especially just before pupation. 2 Broods For each species, we list the months when the caterpillar stage is most likely to occur over most of the eastern United States. Note that caterpillars in the Deep South often appear several weeks be¬ fore the times provided here, and there may be one or more addi¬ tional generations each year. Conversely, to the north, caterpillars may occur later and there may be only one generation each year. Caterpillar Mimicry and Defense The color patterns of caterpillars that feed on exposed foliage are often distinct, even in closely related species. In some genera, such as Acronicta, Datana, and Dasychira, the caterpillars are far more distinctive than adults. The markings and shapes of caterpillars may change between consecutive larval molts—note the difference in appearances of the young and mature caterpillars of the spice- bush swallowtail (pg. 24) and gypsy moth (pg. 11). Our photo¬ graphs are typical for mature larvae. Colors may vary across a species' geographical range, and in some loopers (or inchworms), the color of the caterpillars may vary dramatically with the popu¬ lation density. For example, in both the spring cankerworm and elm spanworm, caterpillars from low-density populations tend to be green, whereas those from outbreak populations are often con¬ siderably darker. Color and adornment may greatly affect a caterpillar's ability to survive predation by birds. For example, caterpillars with promi¬ nent red, orange, and yellow colors (commonly offset with white and black) are avoided by many birds. They also may gain protec¬ tion from hairs or spines or by retaining toxins that they acquire from their host plants. A few species—the io moth, buck moth, and saddleback caterpillar—bear spines that can deliver painful stings. Tussock moths (including the gypsy moth) have glands on two ab¬ dominal segments that manufacture noxious compounds that are loaded onto the body hairs. When handled, the variable oakleaf caterpillar may release enough formic acid to cause skin blisters. Caterpillars palatable to birds tend to be camouflaged, blending masterfully into forest backgrounds. Many green species mimic foliage; some even have false leaf damage incorporated into their coloration. Others that rest on branches or tree trunks by day may resemble twigs and bark. Several imitate the look of fresh, wet bird droppings. Others actively collect debris and attach it to their backs so that they resemble anything but a caterpillar. 3 Palatable and unpalatable caterpillars may have strikingly differ¬ ent behaviors. Palatable species often feed at night and are "neat" feeders that are quick to move off damaged leaves. An extreme example of tidiness is provided by sphinx and underwing caterpil¬ lars, which "cover up their tracks" by clipping away leaves upon which they have fed by chewing through the petiole. In contrast, unpalatable species are often active during the day and frequently rest on or near damaged leaves. Both the coloration and habits of protected species make them obvious and more likely to be noted even by casual observers. As such, more of this type are presented in this booklet. Rearing, Identification, and Preservation If definitive identifications are required, it may be necessary to rear caterpillars to their adult stage, that is, to moths or butterflies. Whenever possible, secure and rear several larvae of a species because parasites and pathogens kill many caterpillars before they reach maturity. Before pupation, it may be helpful to add a half¬ inch layer of lightly moistened (horticultural grade) sphagnum. Sphagnum tends to discourage the growth of molds and slowly gives up moisture to the rearing container, but overly damp sphag¬ num may result in fungal infections. Sphagnum or some other pupation medium is important for species that normally pupate in soil. An extended period of near-freezing temperatures is needed to ensure emergence of the species that do not overwinter as adults. Many helpful suggestions for collecting and rearing cater¬ pillars can be found in Coveil's (1984) Field Guide to the Moths of Eastern North America. It is a good idea to preserve examples of late-instar larvae as vouchers, that is, references, in case subsequent rearing efforts prove futile. Preserve these caterpillars by dropping them into water that has been brought to a boil and leaving them submerged for a few minutes or until the bodies are fully distended. Larvae should then be transferred to 70% ethanol. Less satisfactory results may be obtained by killing caterpillars directly in ethanol or iso¬ propyl (rubbing) alcohol, although such specimens often discolor and are rarely fully distended. Freeze-drying larvae will yield rather shrunken, albeit identifiable, specimens. Preservation tech¬ niques for caterpillars are reviewed in Stehr's (1987) Immature Insects. Because fluid preservation always results in the loss of color, especially greens and yellows, larvae should also be photo¬ graphed to record their colors. 4 Silkworms and Royal Moths (Family Saturniidae) These medium to large caterpillars usually have conspicuous long setae, "horns," or stinging spines. Pest species are often gregarious in early instars. The caterpillars are most often encountered as they are walking over the ground in search of a pupation site. Orange-striped oakworm (.Anisota senatoria) Charcoal with eight orange- yellow stripes. Head black. Second thoracic segment with long, black spinulose horns. Feeding gregariously in early instars, then becoming solitary. Hosts: oaks. Larva: August to October, one generation. Spiny oakworm (Anisota stigma) Light brown, often flushed with pink, speckled with white. Head orange brown. Second thoracic segment with long, black spinulose horns. Gregari¬ ous feeder in early instars, then solitary. Hosts: oak and hazel preferred. Larva: August to October, one generation. Pink-striped oakworm (Anisota virginiensis) Pink with broad dorsal and lat¬ eral charcoal stripes, finely speckled with white. Head orange brown. Second thoracic segment with long, black spinu¬ lose horns. Gregarious in early instars, then solitary. Hosts: various hardwoods, especially oak. Larva: August to October, one generation. 5 Green-striped mapleworm (.Dryocampa rubicunda) Pale green with longitudinal striping. Head bright reddish brown. Second thoracic seg¬ ment with black, spinulose horns. Hosts: occasional pest of maple, but also on oak and other plants growing with maple. Larva: June to Septem¬ ber, two generations in South, one northward. Hickory horned devil (■Citheronia regalis) Our largest and perhaps most spectacular caterpillar. Heavily armored with long stout orange and black dorsal horns on tho¬ racic segments. Abdomen with shorter stout black spines. Hosts: often hickory, walnut, and sweet gum, but also many forest hardwoods. Larva: July to September, one generation. Imperial moth (.Eacles imperialis) Bright green, brown, or pink with long white hairlike setae. First two thoracic segments with short yellow spinulose horns. Spiracles conspicuously encircled with white. Hosts: pines and many hardwoods. Larva: July to September, one generation. 6