Caterpillars are larvae (the "worm" forms) of insects in the order Lepidopterathe butterflies, skippers, and moths. In number of species known, Lepidoptera is the second largest of all insect orders. Consequently, caterpillars are numerous; more than 11,000 species occur in North America, with over 5,000 species in the eastern United States alone. Most caterpillars are plant feeders. They occur on a wide variety of plants, and many are serious pests. Caterpillars are among the most common of all insect forms found on foliage of forest, shade, and ornamental trees.
The typical caterpillar has a distinct head and a cylindrical body composed of thirteen segments. The anterior three body segments constitute the thorax, and each thoracic segment bears a pair of jointed legs. The remaining ten segments make up the abdomen. Typically, abdominal segments three, four, five, six, and ten each bears a pair of unjointed, fleshy projections called prolegs. In some caterpillar groups, however, prolegs may be absent (slug caterpillars) or occur only on segments five, six, and ten or six and ten (loopers). Prolegs are equipped with rows or circles of small hooks called crochets which aid caterpillars in crawling and clinging to surfaces.
Caterpillars come in a variety of shapes, colors, and sizes. Some species are bare, others sparsely to densely clothed with fine setae (hairs); some are drab, others brightly multicolored; some have smooth bodies, others bear one to many tubercles, bristles, spines, and/or horn-like projections. Within the group are found some of the largest and most striking representatives of our native insects. Also, within the group are found CATERPILLARS THAT "STING".
Stinging caterpillars do not sting in the familiar manner of bees, yellowjackets, hornets, and wasps (Order Hymenoptera). In the bee-wasp group, females (only females sting) are equipped with venom glands and stingers (modified ovipositors) with which they penetrate skin and introduce venom. Among the lepidopterans, neither the adult nor the caterpillar possesses this type of sting apparatus. Instead, stinging caterpillars bear specialized nettling or urticaceous setae or spines. These structures are hollow and contain toxins from poison-gland cells to which they are joined. These are primarily defensive structures for protection of caterpillars from predators and other enemies. The sting inflicted on humans is not from a deliberate attack by the caterpillar, but the result of contact, usually inadvertent, with toxin-bearing setae or spines. When brushed against, these structures break away, releasing toxins. In some cases, broken setae may penetrate the skin; in others, toxins spill out to spread on the surface of the skin.
Reactions to contact vary and include: slight to intense nettling, stinging, itching, or burning sensations; development of dermatitis, rash, lesions, or pustules; inflammation, swelling, and numbness at or around the area of contact; fever and nausea; and, in some cases, intense pain. The type of reaction depends on the species of caterpillar, degree of contact, type of toxin, and susceptibility of the individual. Reactions may be especially severe for individuals with allergies or sensitive skin.
The irritation usually results from direct contact with a live caterpillar. However, in some species, urticating setae may retain nettling capabilities for some time after death of the caterpillar. Molted skins and silk cocoons bearing toxic hairs from last-stage larvae may also cause nettling if handled. Nettling caused by contact with dead caterpillars, cast skins, and cocoons is generally milder than that produced by live caterpillars.
Many species of caterpillars are variously armed or clothed with setae and spines; however, only a relative few actually possess venomous or urticating structures. Thus, there are "stingers" and harmless "look-a-likes", and distinguishing one from the other solely on appearance is difficult. Determining which is which by "hands-on" personal bio-assay is foolproof but could be foolhardy and painful.
During years of study of tree insects at the Alabama Agricultural Experiment Station, several species of urticating caterpillars have been encountered and identified. Represented are nine families that contain one or more species known, or reported, to be urticaceous or otherwise capable of causing irritating reactions on contact with human skin. The following is offered as a guide to recognition of stinging caterpillars found on Alabama trees. Also included are some common "dangerous-looking" but harmless caterpillars found on trees and shrubs.
Saddleback Caterpillar (Sibine stimulea) (Photo 1)
The saddleback is one of the most common of slug caterpillars occurring in the area. Its conspicuous form and markings make it nearly unmistakable, even in the early stages of development. The full-grown caterpillar is about 1 inch long. The anterior and posterior areas of the body are dark brown with prominent brown "horns" that bear numerous spines. The middle of the body is green. The green area has a white or cream margin and a large oval to oblong dark brown spot in the center, also with white margin. The appearance is that of a saddle and blanket, thus the common name. Small clumps of spines occur in a row along the lower margin of the green area and at the rear of the caterpillar.
The saddleback is generally a solitary feeder; however, early stage larvae may be somewhat gregarious. The caterpillar occurs on a wide variety of trees, shrubs, and other plants, including corn. Common tree hosts are apple, basswood, cherry, dogwood, elm, maple, oak, and plum. It is most often encountered in late summer and fall. The sting of the saddleback is the most severe of the slug caterpillars.
Hag Moth Caterpillar (Phobetron pithecium) (Photo 2)
The hag moth larva, sometimes called the monkey slug, is distinctive in form and easy to identify. The full-grown caterpillar is brown, hairy, and about 5/8 inch long. Along the body there are nine pairs of fleshy lateral processes which bear hidden urticating setae. The third, fifth, and seventh pairs of processes are long and sometimes twisted. These have been described as resembling "disheveled locks of a hag", apparently the basis for the common name.
The caterpillar is generally a solitary feeder, and will feed on foliage of several trees including apple, ash, birch, dogwood, hickory, oak, and willow. It has been collected from July into fall, but is usually most common in August and September. The specimens pictured were collected from oak in September.
Stinging Rose Caterpillar (Parasa indetermina) (Photo 3)
The full-grown caterpillar is 3/4 to 7/8 inch long; basic color is yellow. The body bears pairs of long, horn-like, bristly spines and clumps of smaller spines which are characteristic of several of the slug caterpillars. A useful identifying characteristic is the broad purplish band down the midline of the back. Within the band are narrow whitish longitudinal lines, which may be interrupted by constrictions in the band. Reddish, white, and purple lines occur along the sides.
Hosts of the stinging rose caterpillar include apple, cottonwood, dogwood, hickory, oak, redbud, sycamore and rose bushes. Larvae are usually found in August. Specimens have been collected in Lee County from cottonwood and oak at the end of August.
Spiny Oak Slug (Euclea delphinii) (Photo 4)
The full-grown larva is about 3/4 inch long. Basic color is yellow-green but color, especially of the pattern on the back, may vary. There are three pairs of large horn-like spines with black-tipped bristles at the front and two pairs at the rear. Clumps of smaller spines occur in rows along the back and sides. There are four dense clumps of small dark spines at the rear end; these are important characteristics for identifying the species.
The caterpillar feeds on foliage of several woody plants including beech, cherry, maple, oak, redbud, sycamore, and willow. It is usually found in late summer and fall. The specimen pictured here was collected from redbud in late September.
Isa textula (Photo 5)
This species has no known common name. Information available on its habits is limited and makes no reference to whether or not the species has stinging capabilities. However, being a slug caterpillar well-equipped with bristled spines, it seems suspect.
*"Hands on" experience has now confirmed that I. textula is a "stinger." LLH.
The full-grown caterpillar is flattened and about 5/8 inch long. Color and markings are as pictured. Tree hosts include cherry, maple, and oak. The species is not common in our area. The specimen pictured was collected in Lee County from sawtooth oak in mid-September.
Nason's Slug (Natada nasoni)1 (Photo 6)
The form of Nason's slug differs from that of the foregoing slugs in that there are no large, conspicuous, horn-like bristled spines present. There are, however, rows or tufts of small spines, some of which are urticating, along the back and sides. The nettling sensation produced is mild and short-lived.
The full-grown caterpillar is 3/4 to 7/8 inch long. Basic color is green; markings are as pictured. Food trees include beech, hickory, hornbeam, oak, and several other trees and shrubs. This caterpillar is not common in our area. The specimen pictured here was collected in Lee County from sawtooth oak in early October.
Larvae of flannel moths feed on a variety of trees and shrubs. Young larvae feed gregariously; older larvae are often found feeding singly. In most years, populations are low and foliage loss minimal; however, some species can become abundant and cause extensive defoliation of trees. Three species of flannel moths are known to occur in the Southeast. Two of these, the puss caterpillar and white flannel moth, are common in Alabama.
Puss Caterpillar (Megalopyge opercularis) (Photo 7)
The puss caterpillar (the adult is called southern flannel moth) is our most "dangerous" stinging caterpillar. Contact may produce severe reactions including: intense burning and nettling of the skin; severe pain; reddening and inflammation; development of pustules and other lesions; numbness; swelling, which may sometimes be extensive; and nausea. Pain may persist from one to twelve or more hours. In some instances, victims have required medical attention. The larva is urticating in all stages, but severity of the reaction is generally proportional to size. Also, newly molted skins retain stinging capabilities.
The caterpillar is thickly covered with fine, long, tan, grayish to brown hairs, among which are hidden venomous setae. Hairs peak roof-like over the back and taper rearward to form a "tail". Hairs along the "ridge" of the back occur in small tufts; on each side are small patches of white. The full-grown larva is about 1 inch long, but with its hairy coat, appears to be much larger. The overall length of the specimen shown at left in Photo 7 is 15/8 inches.
Puss caterpillars feed on foliage of a variety of broadleaf trees and shrubs. Some common tree hosts are apple, elm, hackberry, maple, oak, pecan, and sycamore. Two larval broods likely occur each season in Alabama, one in spring and early summer and one in late summer and fall. It is the caterpillars of the second brood that are most often encountered. Specimens pictured here were collected in Lee County during September.
White Flannel Moth (Norape ovina) (Photo 8)
The full-grown caterpillar of the white flannel moth is 1 to 11/4 inches long. The body is basically pale yellow with a broad, dark brown to black band on the back. Within the band is a double row of raised, pale yellow spots or tubercles which bear clumps of short setae. Similar clumps of setae occur along each side. Overall, the body is sparsely clothed with longer hairs.
This caterpillar is known to feed on redbud, hackberry, beech, mimosa, and honeylocust. In Alabama, it is found most often on redbud and occasionally on honeylocust. Larvae generally begin to appear during the first half of August, and are present into October. Young larvae often feed side-by-side in rows; older larvae tend to scatter and feed individually. The species is sometimes a serious defoliator of ornamental redbud.
Buck Moth Caterpillar (Hemileuca maia) (Photo 9)
All species of caterpillars of the genus Hemileuca are reported to bear urticating spines; only one species, the buck moth, is known to occur in Alabama. The full-grown caterpillar is about 23/8 inches long. The head is dark reddish-brown to black. The body is brown to grayish black, and sprinkled liberally with small yellowish dots. There is a double row of short, tannish tufts of spines down the back and rows of larger, longer, bristled, red to black spines along each side. Young larvae are solid black.
In Alabama, buck moth infestations are found primarily on oak. Caterpillars are usually encountered during May and the first half of June. Severity of sting ranks behind that of the puss caterpillar and is probably about equal to that of the saddleback. Welts raised on the skin may remain visible for a day to more than a week.
Io Moth Caterpillar (Automeris io) (Photo 10)
This caterpillar is a general feeder. Food plants range from grasses and herbs to foliage of some hardwood trees. Some trees reported as hosts include apple, black locust, cherry, dogwood, elm, hackberry, hickory, maple, oak, sycamore, and willow. The full-grown larva is 21/4 to 21/2 inches long and fairly easy to recognize. The head and body are yellowish green; thoracic legs and prolegs are red. There is a broad white line along each side, bordered above by a similar reddish line and below by a thinner (sometimes broken) reddish-purple line. Raised tubercles, each bearing a whorl of green branched spines, occur on each segment along the back.
Two generations probably occur each season, with larvae present during June-October. This caterpillar is scarce in Alabama, and is only rarely encountered on foliage of trees.
Whitemarked Tussock Moth (Orgyia leucostigma) (Photo 11)
The full-grown caterpillar is about 13/8 inches long. The head and upper surface of the segment behind the head are red. There are two long black "pencils" or tufts of hairs on the first segment of the thorax; a single, similar "pencil" occurs at the rear on the eighth abdominal segment. The back is mostly black. There is an erect, brush-like tuft of short, white or yellowish hairs on each of the first four abdominal segments, and a conspicuous red dot on segments six and seven. The sides of the body are yellow, cream, or grayish with fine whitish hairs arising from each segment.
Larvae of the whitemarked tussock moth feed on a wide variety of trees and shrubs. Some common tree hosts are apple, basswood, cottonwood, elm, maple, oak, sycamore, and willow. At least two larval broods occur each season in our area. Caterpillars are generally present from early April into October.
Smeared Dagger Moth (Acronicta oblinita) (Photo 12)
This caterpillar is a general feeder. Food plants include smartweed (the larva is sometimes called the smartweed caterpillar), strawberry, corn, cotton, grasses, clover, and occasionally apple, boxelder, cottonwood, elm, oak, and willow. Cottonwood and willow seem to be the preferred tree hosts in our area.
The full-grown caterpillar is 15/8 to 2 inches long. The body is basically black with a broad, bright yellow, broken line along each side, and a double row of yellow spots down the back. There are rows of black tubercles (some may be red) from which arise numerous yellowish to brown bristly spines.
Two larval broods may occur each season; spring and early summer, and late summer and fall. In Lee County the caterpillar is most often found on its tree hosts in September and October.
Eastern Tent Caterpillar (Malacosoma americanum) (Photo 13)
The eastern tent caterpillar is responsible for the grayish-white tents or webs commonly seen in wild cherry trees each spring. Wild cherry is the primary host, but larvae feed also on apple, crabapple, peach, and pear. The full-grown caterpillar is about 2 inches long. The head is black; the back is mostly black and the sides bluish. There is a continuous light line down the midline of the back, bordered on each side by reddish-brown lines. Caterpillars are present in March and April.
Forest Tent Caterpillar (Malacosoma disstria) (Photo 14)
The forest tent caterpillar, although classified as a tent caterpillar, does not make a tent. Larvae feed on foliage of a variety of trees, but the primary hosts in Alabama are water tupelo, blackgum, sweetgum, and the oaks. The full-grown caterpillar is about 2 inches long. The head is blue, mottled with black. The body is blue to bluish black. The primary identifying characteristic for the caterpillar is a row of whitish diamond- or keyhole - shaped spots down the midline of the back. Larvae are generally present in April and May.
Both species construct similar cocoons for pupation at the end of the larval period. Cocoons (Photo 15) are spindle-shaped and 3/4 to 11/4 inches long. They are usually found in semi-protected situations such as crevices of bark of trees, under leaves and other objects on the ground, sometimes in folded leaves, and in cracks or crevices in walls of nearby buildings.
Laurelcherry Smoky Moth (Neoprocris floridana)* (Photo 16)
Laurelcherry is the caterpillar's primary, perhaps only, host. The full-grown larva is about 1/2 inch long. The back is black with a row of small elongate white spots along the midline, bordered by a double row of larger white segmental bars that form broken lines. The sides are pale yellow, and bear small tufts of short setae. The caterpillar is most common in late summer and fall; the specimen pictured was collected in Lee County during the first week of October. Nettling produced is mild and short-lived; however, small reddish welts may develop at points of contact and remain visible for a few hours.
* Identity supplied by Dr. Gerhard Tarmann (Innsbruk, Austria), who described the species.
Variable Oakleaf Caterpillar (Lochmaeus manteo) (Photo17)
The full-grown caterpillar is approximately 11/2 inches long. The head is greenish with a vertical black stripe on each side, bordered on the outside by a cream to white stripe. The base color of the body is green. There is a narrow yellowish, cream, or white line down the midline of the back, and wider cream or white lines along the edges of the back. Coloration of this back area is highly variable (thus the common name), and ranges from green to reddish brown with gradations between.
The caterpillar is most commonly found on various oaks, but also occurs on basswood, birch, boxelder, elm, and a few other hardwoods. There are two larval broods each season in Alabama, May-June and mid-August to mid-October.
Spiny Elm Caterpillar (Nymphalis antiopa) (Photo 18)
The full-grown caterpillar is about 2 inches long. Its body is black with numerous white flecks and a row of red spots down the back; prolegs are red. Larvae feed on foliage of elm, cottonwood, hackberry, and willow. In our area, it is most often found on elm and willow. In Lee County, caterpillars are usually seen in April and May; however, a second brood may occur, with larvae possibly present again in August-September.
The spiny oakworm (Anisota stigma - Saturniidae) (Photo 21) is sometimes common and abundant on oak, particularly open-grown ornamental and shade trees. The full-grown larva is 13/4 to 21/2 inches long, and bears a pair of long, dangerous-looking but harmless spines on the thorax. Young larvae feed in groups; older larvae tend to scatter and feed singly. The caterpillar is generally most common in August, September, and October. The spiny oakworm is representative of a small group of similarly "horned" caterpillars; the two long, curved spines behind the head (Photo 21, inset) are characteristic of the group. Three other species are common: pinkstriped oakworm, orangestriped oakworm, and greenstriped mapleworm. The common name essentially describes each of these and denotes its primary host.
Hornworms are larvae of sphinx moths, sometimes called hawk moths or hummingbird moths (Family Sphingidae). These are rather large caterpillars, 2 to 4 inches long. Bodies are generally smooth, except for the characteristic sharp, but harmless, spine or "horn" arising from the top of the eighth abdominal segment. Several species of hornworms feed on foliage of trees. Two examples are catalpa sphinx (catawba worm), Ceratomia catalpae, (Photo 22) on catalpa, and waved sphinx, Ceratomia undulosa (Photo 23) on ash.
The sycamore tussock moth (Halysidota harrisii - Arctiidae), fall webworm (Hyphantria cunea - Arctiidae), and walnut caterpillar (Datana integerrima - Notodontidae) are good examples of non-stinging "hairy" caterpillars frequently found on trees. The sycamore tussock moth larva (Photo 24) feeds on leaves of sycamore and London plane trees. The full-grown caterpillar is 1 to 11/8 inches long. It is generally present from early June through September. The fall webworm (Photo 25) is responsible for the silken webs seen surrounding leaves of pecan, persimmon, willow, sweetgum, mulberry, and several other trees. Webs and caterpillars begin to appear in spring but are most abundant in late summer and fall. The full-grown caterpillar is about 11/4 inches long. The walnut caterpillar (Photo 26) is 13/4 to 21/4 inches long when fully grown. Larvae feed in groups on foliage of pecan, walnut, hickory, and butternut. There are two broods each year, with caterpillars present in May-June and again in July-August. The menacing, upright pose pictured at right in Photo 26 is not that of a caterpillar preparing to "strike", but rather is the typical stance assumed by this and other Datana caterpillars when disturbed or alarmed.
Reaction to disturbance, such as that exhibited by Datana larvae (Photo 26), is not uncommon. Several species of caterpillars respond in various ways to noise or motion; some, in so doing may utilize unique specialized structures. Response to disturbance is commonly associated with defense against predators or parasites. Whatever the purpose, action taken often appears ominous and threatening. Two such examples follow.
In one group of notodontid caterpillars, prolegs on the last abdominal segment are long and form tail-like structures called stemapods (Photo 27). In some species, these are extensible and, when the caterpillar is disturbed, are extended and waved about in a threatening manner (Photo 29). The caterpillar pictured (Photo 27) is the larva of the black-etched prominent, Cerura scitiscripta; in Photo 28, the larva of the gray furcula, Furcula cinerea. Both feed on cottonwood and willow and are usually found in late summer and early fall.
The "big-eyed" specimen with swollen "head" and colorful "forked tongue" (Photo 29) is the harmless larva of the common spicebush swallowtail butterfly (Papilio troilus - Papilionidae). The "eyes" are merely spots on the thorax. The "forked tongue" (called osmeterium) is a specialized structure common to papilionid caterpillars. It is normally concealed in the first segment of the thorax, but is extended when the larva is touched or disturbed. The full-grown caterpillar (Photo 30) is 13/4 to 2 inches long. It is commonly found on spicebush, sassafras, and yellow-poplar.
Neither the stemapods of notodontids nor osmeteria of swallowtails are known to be harmful to humans; however, osmeteria, when extended, give off a musty odor.
Among the caterpillars reviewed, the saddleback, buck moth caterpillar, and puss caterpillar are considered our most serious stingers. And among these, the puss caterpillar produces the most severe reaction (See description under the species). Treatment of sting areas with ice packs or ammonia may give some relief from pain. However, for severe reactions, victims should promptly seek medical attention.
Matheson, Robert. 1950. Medical Entomology. Comstock Publishing Company, Inc. Ithaca, New York.
Stehr, F. W. 1987. Immature Insects. Kendall/Hunt Publishing. Dubuque, Iowa.
USDA Forestry Service (Drooz, A.T., ed.). 1985. Insects of Eastern Forests. Misc. Publ. 1426.
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Photos courtesy of Lacy L. Hyche