Version May 2024
INTRODUCTION — "Lepidopterism" is the term for a variety of cutaneous and systemic reactions that result from contact with larvae (ie, caterpillars) or adult forms of moths and butterflies (order, Lepidoptera) (table 1). "Erucism" (from Latin "eruca," caterpillar) is another term used to refer to reactions from contact with caterpillars.
The primary clinical manifestations of lepidopterism include sting reactions, hypersensitivity reactions, and lonomism, a potentially life-threatening hemorrhagic diathesis. The diagnosis is straightforward in many patients due to a history of contact with caterpillars or moths followed closely by the onset of symptoms.
Most sting and hypersensitivity reactions are mild and self-limited and can be managed with measures for symptomatic relief. In contrast, patients with lonomism often require inpatient supportive care and prompt medical intervention.
The clinical features, diagnosis, and management of lepidopterism will be reviewed here. Bites and stings from other insects are reviewed separately. (See "Insect and other arthropod bites" and "Bee, yellow jacket, wasp, and other Hymenoptera stings: Reaction types and acute management" and "Bedbugs".)
EPIDEMIOLOGY AND RISK FACTORS — There are few epidemiologic studies of lepidopterism. Because many reactions are self-limited and mild, and because many human-insect encounters occur in tropical areas with poor health care access, lepidopterism is probably underreported.
Most episodes of lepidopterism are isolated and sporadic; however, temporal, occupational, and geographic factors may influence risk for development. Several medically important species are periodically subject to dramatic variation in density, resulting in infestations of large numbers of caterpillars or moths and subsequent outbreaks of coincident cases [1-7]. Individuals who work in rural areas (eg, forestry workers, farmers, entomologists, and gardeners), particularly during warmer months, are at higher risk of exposure [2,8,9]. Outbreaks of hypersensitivity reactions to Lepidoptera have also been reported in urban and suburban environments, particularly near parks or schools with heavily infested trees [10-14].
In areas where processionary caterpillars (Thaumetopoea spp) are present, cutaneous reactions can be frequent [12-14]. In a survey of 1224 adults in an endemic area for the pine processionary moth (Thaumetopoea pityocampa) in Spain, the estimated point prevalences of cutaneous reactions to this species were 12, 10, and 4 percent among inhabitants of rural, semi-urban, and urban areas, respectively [14]. Global warming and changes in land-use patterns have been linked to range expansion of oak processionary caterpillars (Thaumetopoea processionea) into Northern and Western Europe [15].
In Venezuela, periodic fluctuations in yellowtail moths (Hylesia spp), which tend to congregate around artificial lights, have been associated with high numbers of patients with dermatitis [4,6]. Reactions to Lonomia caterpillars have risen in Brazil [16], likely due to extensive deforestation and increasing human settlement of remote areas.
TYPES OF REACTIONS — Of the more than 150,000 known species of Lepidoptera, only a relative few are reported to cause significant adverse reactions in humans. The clinical manifestations can largely be divided into three main groups:
●Sting reactions
●Hypersensitivity reactions
●Lonomism (bleeding diathesis)
Sting reactions — Sting reactions are short-lived, painful reactions resulting from contact with venom in caterpillar spines. Numerous species of caterpillars bear spines capable of inflicting a painful sting (table 1). Caterpillar spines are often paired, clustered, or branched and may be hollow.
Entomology and pathogenesis — Stinging caterpillars largely belong to three families of moths:
●Hemileucinae, a subfamily of silk moths found from southern Canada to the southern tip of South America. There are over 600 known species, all of which are likely capable of inducing sting reactions. These large caterpillars bear numerous branched spines that are morphologically consistent across the subfamily (picture 1A-D) [17].
●Limacodidae (slug moths), with over 1600 species found worldwide [18]. Numerous species are known to cause painful stings (picture 2A-D).
●Megalopygidae (flannel moths), found in North and South America. There are over 200 species [18]. These caterpillars are covered in dense fur that hides pairs of highly venomous spines (picture 3).
The content of caterpillar venom is poorly studied but likely contains a broad variety of bioactive proteins [19]. The venom of Lonomia is better understood, and an antivenom has been developed for Lonomia obliqua. (See 'Lonomism' below and 'Management' below.)
Clinical manifestations — Victims are usually stung in exposed areas, such as the neck above the shirt collar (where caterpillars may land when falling from a tree), arms, hands, and feet [20-22]. Typical symptoms include mild to moderate stinging or burning pain that is associated with welts, vesicles, or red papules and plaques at the site of envenomation [20-23]. Characteristically, the paired spines of Megalopyge (flannel moth) caterpillars cause a grid-like or "tram-track" pattern of hemorrhagic papules (picture 4).
Pain usually persists for minutes to a few hours. Occasionally, pain is severe or incapacitating, particularly from stings of Megalopyge species. Stings from caterpillars of the southern flannel moth (Megalopyge opercularis, also called the asp or puss caterpillar) may result in severe radiating pain, swelling of the affected limb, and occasionally systemic symptoms such as headache, fever, adenopathy, nausea and vomiting, abdominal pain, or chest pain [24-26].
Diagnosis — The diagnosis is made based upon a history of contact with a stinging caterpillar and consistent clinical manifestations. Recognition of the classic "tram-track" pattern of hemorrhagic papules is helpful for diagnosis of Megalopyge stings (picture 4).
The differential diagnosis for caterpillar stings includes envenomation by other insects, including bees and wasps, snakes, or other animal bites. In many cases, it is impossible to distinguish these entities without appropriate history. (See "Bee, yellow jacket, wasp, and other Hymenoptera stings: Reaction types and acute management" and "Snakebites worldwide: Clinical manifestations and diagnosis".)
Hypersensitivity reactions — Hypersensitivity reactions can result from mucocutaneous contact with a broad range of caterpillars or, in some cases, moths (table 1).
Entomology and pathogenesis — The caterpillars that cause hypersensitivity reactions tend to be "hairy," bearing numerous hair-like setae. Setae may help to protect the soft-bodied larvae against predators. Numerous families of Lepidoptera utilize this defensive technique, including common species such as the Lymantria dispar caterpillar (formerly known as the gypsy moth caterpillar (picture 5)), wooly bear caterpillar, tussock moth caterpillars (picture 6), and processionary caterpillars. Exposure to setae on Hylesia moths (picture 7) also can cause a hypersensitivity reaction ("Caripito itch" or "papillonite"), with occurrences reported in Venezuela; French Guiana; Cozumel, Mexico; Brazil; Argentina; Uruguay; Guyana; and Peru. Contact with Euproctis moths in Singapore has caused similar symptoms [5].
Reactions typically occur after direct contact with caterpillars or moths. However, when offensive moths or caterpillars are found in high numbers, their setae can be transported by wind or other fomites (towels, clothing, etc), causing symptoms without known direct contact [6,10,11,14]. In particular, processionary caterpillar setae may last in soil, on tree bark, or embedded in silk cocoons spun by the caterpillar and cause reactions months after caterpillars are found [10]. Setae from Hylesia species can be found on egg masses; abdominal setae on female Hylesia moths are transferred to eggs for protection.
The pathophysiology behind these reactions is poorly understood and may vary from species to species. In some cases, it is likely that symptoms result from a combination of mechanical irritation and a mixed type I/type IV hypersensitivity reaction. The chitinous setae penetrate the skin and minute amounts of protein allergen are thus exposed to the immune system, resulting in allergic reactions. Processionary caterpillar setae are sharp and barbed and contain at least seven separate proteins capable of inducing an allergic response. An immunoglobulin E (IgE)-dependent immediate wheal formation from T. pityocampa (pine processionary caterpillar) extract prick testing has been repeatedly demonstrated [8,9,27-29]. Setae and setae extracts have also been shown to stimulate T lymphocytes [30].
Clinical manifestations — Typically, symptoms are described as itchy papules, urticarial wheals, or a pruritic dermatitis that occurs within minutes or hours after contact and lasts for one to several days. Exposed areas such as the hands, feet, neck, and face are often affected preferentially (picture 8A-C). In some patients, reactions are severe and widespread [2,3,5,6,8,10-12,28,31,32]. Rarely, symptoms persist for weeks or months [6,33].
In addition to the more common reactions, anaphylaxis and angioedema have been reported [8]. Contact with mucous membranes (eg, when a child puts a caterpillar in his/her mouth or from airborne setae) may cause dysphagia, erythema, pain, edema, drooling, pruritus, rhinitis, conjunctivitis, dyspnea, and shortness of breath [2,8,10-12,31].
Diagnosis — The diagnosis of a caterpillar hypersensitivity reaction is typically straightforward, with onset of symptoms within a few hours of contact with caterpillars or moths, often confined to the area of contact. However, where infestation is heavy, environmental contamination with offensive setae may cause widespread symptoms even without direct contact. In this situation, a high index of suspicion is needed for diagnosis.
The differential diagnosis includes other causes of allergic or irritant contact dermatitis, atopic dermatitis, phytophotodermatitis, and scabies. If symptoms are persistent, patch testing may be needed to evaluate for occult contact dermatitis. Examination for burrows and skin scraping can be used to exclude scabies infestation. (See "Irritant contact dermatitis in adults" and "Clinical features and diagnosis of allergic contact dermatitis" and "Allergic contact dermatitis in children" and "Photosensitivity disorders (photodermatoses): Clinical manifestations, diagnosis, and treatment", section on 'Phytophotodermatitis' and "Scabies: Epidemiology, clinical features, and diagnosis".)
Lonomism — Lonomism is a hemorrhagic diathesis that can result from stings from some Lonomia species (table 1).
Entomology and pathogenesis — Lonomism is caused by stings from two closely related species of South American caterpillars (Lonomia achelous, found in Venezuela and Guinea, and L. obliqua, found largely in southern Brazil) (picture 9A-B). There are at least 11 species of Lonomia, and it is unknown whether contact with other species causes similar pathology [17]. The gregarious caterpillars are often found on tree trunks near the ground during the day.
Envenomation by way of hollow, branched spines causes a hemorrhagic diathesis that is fatal in approximately 4 percent of affected patients [34]. Lonomia caterpillar venom from both species contains serum proteases that degrade fibrin, fibrinogen, and factor XIII, while prothrombin is activated [35-38].
Clinical manifestations — Lonomia stings commonly occur on the hand or foot and cause severe pain at the site of envenomation, followed by dizziness, headache, nausea, vomiting, and abdominal pain [34,39]. Clinically evident hemorrhagic manifestations, such as bleeding gums, ecchymosis, bleeding from recent wounds, epistaxis, and hematuria, may also occur [39,40]. In a series of 105 patients with lonomism, at least one of these hemorrhagic manifestations was present in 24 patients (23 percent) at the time of hospital admission [39]. Renal failure, which is reversible in 90 percent of patients, is estimated to occur in 2 percent of patients stung by L. obliqua and is more common in patients stung by a high number (>50) of caterpillars [34]. Death may result from cerebral or pulmonary hemorrhage, renal failure, or other internal bleeding.
Diagnosis — The diagnosis of lonomism is made based upon known or potential exposure to Lonomia species, consistent clinical or laboratory findings, and the exclusion of other bleeding disorders. Expected laboratory findings include low or absent fibrinogen levels, low plasminogen levels, and low levels of factors V, VIII, and XIII. Profound reduction in factor XIII is common in L. achelous envenomation [37,41]. Other laboratory abnormalities associated with lonomism include increased fibrinogen degradation products, increased thrombin-antithrombin complexes, prolonged prothrombin time (PT) and activated partial thromboplastin time (aPTT), and occasionally increased von Willebrand factor [39,41]. Platelet counts are typically unaffected but may be reduced [34]. Renal function may be reduced [34].
Lonomism can resemble hereditary bleeding disorders, disseminated intravascular coagulation (DIC), or snakebite envenomation. Hereditary bleeding disorders usually can be identified by a history of recurrent bleeding, including hemarthrosis, epistaxis, and menorrhagia. DIC is due to an underlying disorder, such as malignancy, sepsis, trauma, or obstetrical complication. DIC may be differentiated by identification of the underlying disorder and by the presence of thrombocytopenia and hemolytic anemia, both of which are uncommon in lonomism. The venom of many snake species can cause consumptive coagulopathy very similar to lonomism. (See "Approach to the adult with a suspected bleeding disorder" and "Approach to the child with bleeding symptoms" and "Evaluation and management of disseminated intravascular coagulation (DIC) in adults" and "Disseminated intravascular coagulation in infants and children" and "Snakebites worldwide: Clinical manifestations and diagnosis".)
MANAGEMENT — Most reactions to Lepidoptera are mild and self-limited and require only removal of visible embedded setae or spines and measures for symptomatic relief. Interventions for lepidopterism have not been evaluated in randomized trials. Recommendations are primarily derived from case reports and small case series:
●Removal of setae and spines – If embedded setae or spines are visible, reasonable attempts at removal via tape-stripping or manual extraction (ie, with forceps) are recommended based upon the theory that doing so may reduce the duration of symptoms [21-23,31,42]. Complete removal of setae is sometimes impossible. Often, remaining hairs and spines will extricate themselves over a period of days.
Setae in the oral or ocular mucosa should be approached similarly, with reasonable attempts to remove spines or setae. In some patients, setae are deeply embedded and difficult to visualize, necessitating laryngoscopy, bronchoscopy, or esophagoscopy [31]. Patients with ocular exposure should be referred to an ophthalmologist for the management of ocular setae.
●Sting reactions – Pain from caterpillar envenomation usually resolves within hours and may be treated with ice or topical and oral analgesia [43]. Narcotics are rarely indicated, even after Megalopyge stings [21,25].
●Hypersensitivity reactions – A variety of interventions aimed at reducing symptoms have seemed helpful in clinical practice [11,14]; however, there are insufficient data to confirm efficacy. If symptom relief is needed, patients with urticarial reactions may benefit from oral antihistamines. Topical antipruritic agents (eg, agents containing pramoxine, camphor, or menthol) and/or a two-week course of a medium to high-potency topical corticosteroid (table 2) may be tried for pruritus associated with other hypersensitivity eruptions. Patients with widespread or severe skin involvement can be given a short course of oral glucocorticoids (eg, 1 mg/kg prednisone taper given over 7 to 10 days).
●Lonomism – Treatment of lonomism typically requires inpatient supportive care and consultation with a hematologist. Rapid administration of an antilonomic serum developed in Brazil for envenomation by L. obliqua appears effective for reversing coagulation time and may reduce fatalities, although data are limited [34,40]. An analysis of data from a cohort of patients in southern Brazil with complications from contact with L. obliqua between 1989 and 2003 found fewer fatalities after antilonomic serum was introduced to treatment regimens. Among the 175 patients managed without antilonomic serum prior to 1995, seven (4 percent) died [34]. In contrast, after 1995, when all patients were treated with antilonomic serum, none of 1892 patients died.
The antilonomic serum (heterologous immunoglobulin against L. obliqua venom) is given intravenously in a single treatment session. Limited data preclude definitive conclusions on the optimal administration. A Brazilian trial in which 44 patients who developed laboratory evidence of hemorrhagic syndrome (with or without clinical signs of hemorrhage) after contact with L. obliqua were randomly assigned to either 10.5 mg or 17.5 mg of antilonomic serum found similar laboratory and clinical outcomes for patients in both groups [40]. No important complications occurred in either group, and all patients recovered completely. Anaphylactic and anaphylactoid complications are potential risks of this therapy.
No antivenom has been developed against L. achelous. Clinical experience supports treatment with antifibrinolytic therapy with aprotinin or aminocaproic acid, while blood replacement products (cryoprecipitate, fresh frozen plasma, whole blood) may cause worsening of symptoms and should be avoided [41].
PREVENTION — Avoidance of areas with heavy infestation of caterpillars or moths known to cause hypersensitivity reactions may decrease risk for lepidopterism. If contact cannot be avoided for occupational or other reasons, gloves and appropriate clothing to minimize skin exposure can be worn. Clothing that may have come in contact with Lepidoptera or setae should be promptly removed after exposure.
SUMMARY AND RECOMMENDATIONS
●The term "lepidopterism" describes a group of reactions that occur secondary to contact with caterpillars, moths, or butterflies. The major types of reactions include sting reactions, hypersensitivity reactions, and lonomism (table 1). (See 'Types of reactions' above.)
●Sting reactions can occur from contact with caterpillars bearing spines. Caterpillars of three families of moths are primarily responsible for sting reactions, Hemileucinae (silk moths), Limacodidae (slug moths), and Megalopygidae (flannel moths). Sting reactions typically cause pain that persists for hours. Occasionally, pain is severe. (See 'Sting reactions' above.)
●Hypersensitivity reactions usually occur in response to contact with caterpillars or moths that bear numerous hair-like setae. Reactions may also occur from contact with dislodged setae in the environment. Patients typically present with itchy papules, urticarial wheals, or a pruritic dermatitis (picture 8A-C). (See 'Hypersensitivity reactions' above.)
●Stings from Lonomia achelous and Lonomia obliqua caterpillars can result in lonomism, a potentially fatal disorder. Patients typically develop severe pain at the site of envenomation, followed by dizziness, headache, nausea, vomiting, and abdominal pain. A hemorrhagic diathesis and renal failure can occur. (See 'Lonomism' above.)
●Most patients with lepidopterism do not require aggressive treatment. Visible spines and setae embedded in the skin should be removed. Analgesics can help relieve pain from stings. Oral antihistamines, topical antipruritic agents, and topical corticosteroids may help relieve pruritus associated with hypersensitivity reactions. (See 'Management' above.)
●Patients with lonomism usually require inpatient supportive care and prompt medical intervention. We suggest treatment of L. obliqua envenomation with antilonomic serum (Grade 2C). Patients with L. achelous stings may benefit from treatment with antifibrinolytics.
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