Urticating Caterpillars

The three most important lepidopteran families with stinging caterpillars are Limacodidae, Megalopygidae, and Saturniidae. Other families include Lymantriidae, Arctiidae, Lasiocampidae, Noctuidae, Thaumetopeidae, Nymphalidae, and Morphoidae. With the exception of the last two families, all are moths as aduits,

Megalopygidae

Members of this family are called flannel moths, referring to the densely hairy adults and larvae. They occur in the Palearctic and Nearctic regions, but especially in South America and the West Indies, where the urticating larvae are known as tataranas, meaning "like fire," cuy machu-cuy, and fire caterpillars. All megalopygid larvae are protected by poisonous spines concealed beneath the more conspicuous long, fine hairs. These are generally type 11 spine hairs which cause a nettling sensation on contact widi skin. Some species can cause particularly severe reactions and present occupational hazards for tree-plantation workers in parts of South America.

Among the 11 species in North America, the southern flannel moth (Megalopyge opercularis) is the most commonly encountered by humans. The larva is called a puss caterpillar, referring to its very hairy appearance (Fig. 18.6). The dense, fine, silky hairs vary in color from

EIGURE 18,6 Puss caterpillar, Megalopyge opercularis (Megalopygidae). (Photo by Sturgis McKeever.)

tan to dark brown or charcoal gray, with one or more pairs of small, dorsolateral patches of white setae. The hairs at the posterior end form a tail-like tuft, whereas the head is concealed beneath the mouselike pelage. It occurs primarily in the southeastern and south-central United States, where the larvae feed on oaks, hackberry, persimmon, apple, orange, almond, pecan, roses, and other trees and shrubs. The short, toxic spines are arranged in radiating clusters (Fig. 18.4C) on three pairs of elevated, longitudinal ridges along the middorsum and sides of the body. The tips of these spines break off on contact with the skin, releasing toxin from the bulbous cavity at their base. All instars are capable of stinging.

The puss caterpillar causes the most painful and severe reactions among urticating species in the United States. Reactions typically include an initial burning sensation, commonly followed by numbness and occasional localized swelling, nausea, and vomiting. Reddened blotches or motding develop at the contact site, often associated with a glistening appearance as cell fluids are released at the skin surface. Edema may occur, especially if the wrist or lower arm is involved; in such cases, the entire limb from hand to shoulder may become swollen. This is often accompanied by inflammation of lymphatic vessels and dull, throbbing aches involving the axillary nodes which may persist for 12 hr or more. Stings on the neck can be particularly severe. Occasionally, when populations of M. opercularis are unusually high, large numbers of people may be affected. Two such instances have occurred in Texas. One involved hundreds of children and resulted in the closing of public schools (Bishopp, 1923); the other was a widespread outbreak in which over 2100 cases were reported (Keegan, 1963).

Other megalopygid species which as larvae cause urticaria in North America are the crinkled or black-waved flannel moth (Lagoa crispata), yellow flannel moth

FIGURE 18.7 White-flannel moth, Norape ovina (Limacodidae). (Photo by G. R. Mullen.)

(L, pyxidifera), and white flannel moth (Norupe ovina) (Fig. 18.7).

Limacodidae (Cochlidiidae, Eucleidae)

This is a large, mostly tropical and subtropical family of moths which occurs widely throughout the Neotropical, Ethiopian, Indo-Australian, and Palearctic regions. Approximately 50 species occur in North America. The larvae are called slug caterpillars or nettle grubs, referring to their unusual shape and the fact that most species have stinging spicule hairs. The larvae are usually somewhat flattened or sluglike, with a small retractable head, short thoracic legs, and reduced abdominal prolegs which are modified as suckers. They move in a gliding motion, suggestive of slugs. The poisonous setae are usually type 4 or type 5 spicule hairs, often in the form of starlike clusters of prickles borne on cone-shaped protuberances; the spines break off easily on contact to cause a nettling sensation.

Six species ofurticating slug caterpillars occur in North America. The most commonly encountered is the saddleback caterpillar (Sibine stimulea). It is easily recognized by a dorsal, brown oval spot with a white border, in turn surrounded by a green area suggesting a saddle and saddle blanket (Fig. 18.8). Urticating hairs are borne on two pairs of large, dark brown, fleshy protuberances (Fig, 18.4J), one pair at each end, and on smaller prominences along the sides. In addition, two pairs of rounded lobes bearing specialized, deciduous setae called calytropes that cause irritation to the skin are located at the caudal end. The stinging reaction consists of a burning sensation and an erythematous lesion which is usually much less severe than that of the puss caterpillar. The saddleback caterpillar is found on oaks, elms, dogwoods, linden, corn, ixora, asters, blueberries, grapes, and a number of fruit trees such as apple, citrus, pear, plum, and banana.

FIGURE 18.8 Saddleback caterpillar, Sibine stimulea. (Limacodidae). (Photo by Sturgis McKcever.)

Larvae of the hag moth (Phobetron pithecium) are sometimes called monkey slugs. Their unkempt, haglike appearance is attributed to their lateral fleshy processes of variable lengths which are covered with fine, brown or grayish plumose hairs (Pig. 18.9). The relatively few, tubercu-late stinging hairs (Fig. 18.4F) are located at the tips of the processes and laterally on each segment. Contrary to some reports in the literature, the urticarial reaction to hag moth larvae is mild, at most. The urticaria is similar to that caused by the saddleback caterpillar. The larvae feed on ashes, birches, hickories, oaks, chestnut, willows, apple, and persimmon.

Another urticating species is the spiny oak caterpillar (Euclea delphinii) in the eastern United States

FIGURE 18.9 Hag moth, Phobetron pithecium (Limacodidae). (Photo by Sturgis McKcever.)

nettling sensation when they contact skin. They also are incorporated into the silken cocoon which the larva spins, thereby protecting the pupa from potential enemies. The adult female possesses similarly specialized hairs on her abdomen which she uses to cover her egg masses while ovipositing. Thus, all developmental stages of the brown-tail moth are provided with stinging hairs which can cause urticaria in humans and other animals.

The gypsy moth (Lymantria dispar) is similar in many respects to the brown-tail moth. Following its introduction to the United States from Europe about 1868, in an unsuccessful effort to use this species for developing a silk industry in Massachusetts, the gypsy moth cscaped and became established in New England. It since has spread widely throughout much of northeastern and Great Lakes area of the United States. The larvae feed on a wide range of deciduous trees, causing extensive damage when their populations are high. They prefer oaks but also attack apple, basswood, alder, birches, boxelder, poplars, willows, hazelnut, mountain-ash, sumac, witch-hazel, and roses. The larvae are quite hairy, with a pair of blue tubercles on each of the thoracic and first two abdominal segments; a pair of red tubercles is present on the next six abdominal segments (Fig. 18.16).

Gypsy moth larvae possess two types of defensive setae. One causes irritation to the skin primarily due to mechanical damage by tiny projections on the long, slender shaft of each seta. The other type is represented by shorter, smoothly tapered setae which arise from a ball-in-socket joint; they are connected with poison glands which apparently produce histamine. Reactions to these stinging hairs vary from mild to moderately severe pruritus with accompanying erythema and papule formation. The onset of discomfort is usually noticed within 8-12 hr after contact, often becoming more pronounced 1—2 days later. Most cases resolve in a few days or up to 2 weeks. Delayed hypersensitivity reactions sometimes result in irritation to the eyes, inflammation of the nasal passages, and shortness of breath. This is especially common in the case of airborne hairs of adult gypsy moths, or

FIGURE 18.16 Gypsy moth, Lymantria dispar (Lymantriidae). (Courtesy of US Department of Agriculture, Forest Service.)

contact with clothes hanging on outdoor lines when this moth is locally abundant. A major infestation of the gypsy moth in the northeastern United States in 1981 resulted in diousands of cases of pruritic dermatitis being reported that year. Like the brown-tail moth, female gypsy moths cover their egg masses with specialized body hairs that can cause urticaria upon contact with skin.

Other lymantriid species which cause urticaria in North America are the whitemarked tussock moth (Orgyia leu-costigma) and the yellow-tailed moth or mulberry tussock moth (Euproctis. similis). Wind-dispersed hairs of E. similis resulted in an estimated 500,000 human cases of pruritic dermatitis in Shanghai, China, in 1981. A similar outbreak involving the Oriental tussock moth (E. flava) affected more than 200,000 people in Japan in 1955, The airborne setae are believed to have originated from larval hairs woven into the cocoon that adhered to the adult moths as they emerged. The pale tussock moth (Dasychira pudibunda) has been reported as the cause of hop dermatitis m Europe.

The adults of this family are known as tiger moths. The larvae usually are covered with fairly dense hairs of varying colors arising from raised warts, in contrast to the normally bare, shiny head. Included in this group is the familiar "wooly bear" caterpillar of the Isabella tiger moth (Pyrrharctia Isabella), which, like most arctiids, does not possess urticating hairs or spines. In larvae that cause skin irritation, type 8 spicule hairs are borne on dorsal tufts, partially concealed by the longer body hairs. Members of the following six genera in North America include urticating caterpillars: Adolia, Callimorpha, Euchaetes, Halysidota, Lophocampa, and Parasemia. Most of these species are relatively uncommon and are only occasionally involved in urticarial cases. The milkweed moth (Euchaetes egle) is perhaps the best known. Its larvae are common on milkweed and are distinguished by dense tufts of black, yellow, and white hairs. Larvae of the hickory halysidota (Halysidota caryae), as the name implies, are found on hickories.

Although the family is cosmopolitan, the largest diversity of arctiid moths occurs in the Neotropical and Oriental regions. Where abundant, they can cause occupational erucism among field workers, as in the case of Premotis semirrufa in South America.

Members of this family are commonly called tent caterpillars or lappet moths. The larvae are usually very hairy and often colorful, with longitudinal stripes. In the case of lappet moths, the larvae are somewhat flattened with hair-covered, fleshy lobes (Jappets) on the sides of each segment. They are typically gregarious, forming communal

Lasiocampidae

Arctiidae

structures are typical type 8 spine hairs. Caterpillars are found on elm, hackberry, poplar, willow, rose, and other common host plants.

Morphoidae

This family includes the showy, brightly iridescent-blue morpho butterflies which occur only in the Neotrop-ics. The larvae of at least seven species are known to cause urticaria: Morpho achillaena, M. anaxibia, M. cypri, M. hercules, M. laertes, M. menelaus, and M. rhetenor (Rotberg, 1971) Most encounters involve accidentally brushing against the larvae feeding on plants in the families Leguminosae and Menispermaceae. Cases are relatively few. They can occur any rime of the year but are most commonly seen during the summer when larval populations are highest. Little is known about the nature of the urticating structures.

Lachryphagous Moths

More than 100 species of zoophilous moths have been observed feeding on lachrymal secretions (Figs. 18.18 and 18.19), primarily in Thailand, Malaysia, and other parts of Southeast Asia (see Banziger references). Most of these moths are members of the Geometridae, Pyrali-dae, and Notodontidae, with a few species of Noctuidae, Sphingidae, and Thyatiridae.

Geometridae

Members of only a few of the 2700 genera of geometrid moths are reportedly zoophilous. Nonetheless, this family includes the largest number of lachryphagous taxa,

FIGURE 18.18 Three species of moths feeding on eye secretions of zebu: Hypochrosis irrorata (Geometridae), RlodesmirificaLis(2yri\\Aze.), and Lobocraspis¿¡riseifusa (Noctuidae). (Photo by Hans Banziger.)
FrGUR.fi 18.19 Lachryphagous moth, Chaeopsestis ludovicae (Thyatiridae), feeding at eye of zebu, (Photo by Hans Banziger.)

with more than 50 species in Southeast Asia. As in other zoophilous moths, except some Noctuidae, only the males are attracted to animals. Most of them feed on mammalian body fluids which either drop to the ground or are smeared on vegetation. They have been observed primarily in association with water buffalo, but other ungulates and elephants also are frequently visited. A few species have been reported imbibing droplets of blood extruded by mosquitoes as they feed on host animals. As a group they do not commonly frequent the eyes; however, Hypochrosis hyadaria, H. flavifusata, Godonela eleonora, and, to a lesser extent, other Hypochrosis, Godonela, Scapula, Problepsis, and Zythos species are locally among the more frequent tear drinkers. The only lachryphagous species that has been reported in the United States is the pectinate euchlaena or forked euchlaena (Euchlaena pecti-naria), observed feeding on eye secretions of a horse in Arkansas (Selman, 1972).

Pyralidae

Pyralid moths are second only to the Geometridae in the number of species known to feed on lachrymal secretions. Members of the following genera are zoophilous and to various extents lachryphagous: Botyodes, Epipagis, Hemis-copis, Lamprophaia, Pagyda, Pyrausta, and Thliptoceras. Microstega- homoculorum, Filodes mirificalis, and Palijya damastesalis are among the more common visitors of human eyes, while Thliptoceras and Hemiscopis tend to suck human perspiration, Typically, however, they have been observed feeding on lachrymal and skin secretions of ungulates and elephants.

Notodontidae

Adult males of at least eight species of the genera Tar-solepis, Togarishctchia, and Pydnella are lachryphagous.

FIGURE 18.21 Two wound-feeding moths, Hypochwsis pyrrhophasata, and Zythos sp. (Geometridae), feeding at site of host injury. (Photo by Hans Banziger.)

FIGURE 18.20 Tear-drinking moth, Chaeopsestis htdovicae (Thyatiri-dae), feeding from human eye with tip of proboscis just inside lower eyelid. (Photo by Hans Banziger.)

Elephants appear to be their preferred hosts; however, these moths feed on a wide range of other large mammals in Southeast Asia, including water buffalo, zebu, tapir, rhinoceros, deer, and humans. Although they feed primarily on tears, they also have been seen imbibing saliva from around the mouth. They are persistent feeders. Some cause only mild discomfort to their hosts, while others are very irritating.

Noctuidae

Although only a few species among the more than 3800 genera of noctuid moths are zoophilous, they are beha-vioraliy the most advanced in terms of lachryphagy and locally can be the most frequent tear drinkers. The highly flexible proboscis is swept back and forth across the eye to induce tearing as the moth feeds. The extra length of the proboscis allows these moths to feed between the eyelids of dozing animals and reduces the risk of being dislodged by eyelid movements of wakeful hosts. Both males and females of Arcyophora and Lobocraspis species are lachryphagous and are the only known tear drinkers capable of digesting proteins contained in lachrymal fluids.

Sphingidae

Rhagastis olivacea in Thailand is the only sphingid moth confirmed as being lachryphagous. It feeds while hovering about the eyes of horses, mules, and humans. It also has been observed inserting its proboscis between the lips and into the nostrils of humans to feed on saliva and nasal secretions; the latter has been described as causing a tickling sensation. Only mild discomfort is experienced when they feed on eyes.

FIGURE 18.20 Tear-drinking moth, Chaeopsestis htdovicae (Thyatiri-dae), feeding from human eye with tip of proboscis just inside lower eyelid. (Photo by Hans Banziger.)

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