More than 165,000 species of caterpillars in the order Lepidoptera (phylum Arthropoda, class Insecta) exist. About 150 are of medical importance. This importance lies in the ability of many species to induce an irritant or toxic dermatitis in humans and in the ability of some species to sting. Caterpillars are the larval forms of moths and butterflies. After hatching from their eggs, caterpillars pass through 4-5 instars (stages between molts) before they pupate in a cocoon. The adult moth or butterfly emerges from the cocoon to reproduce the next generation. More than 50 species in the United States alone are capable of inflicting a painful sting. Seasonal epidemics of dermatitis can occur when caterpillars are numerous.
The most dangerous caterpillar in the United States is the puss caterpillar or asp (Megalopyge opercularis; shown in the image below), the larval form of the flannel moth. It is found throughout the Southeast, from Maryland to Mexico. Stings from this species are common from June through September.
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Caterpillar envenomations. Puss caterpillar or asp. Photo courtesy of the Arizona Poison and Drug Information Center.
Human disease from caterpillars or moths usually arises from direct contact, exposure to substances or animals that have been infested with caterpillars or their webs, or contact with airborne caterpillar debris.
Diaz classifies the diseases caused by caterpillars into 5 groups: erucism, lepidopterism, dendrolimiasis, ophthalmia nodosa, and consumptive coagulopathy with secondary fibrinolysis.
Erucism (caterpillar dermatitis) is characterized by a localized, pruritic, maculopapular contact dermatitis and urticaria, and follows contact with toxic hairs, spines, or hemolymph, either directly or following aerosolization.
Lepidopterism is a systemic illness that occurs following such contact, and it is typified by diffuse urticaria, upper airway inflammation, nausea, vomiting, headache, and bronchospasm.
Dendrolimiasis is a more chronic illness that follows contact with the Asian Dendorlimus pini caterpillar. Patients with this disorder demonstrate a pruritic maculopapular rash and migratory polyarthritis/polychondritis, which can progress to chronic osteoarthritis. Occasionally, acute scleritis occurs as well.
Ophthalmia nodosa presents with acute conjunctivitis, progressing to panophthalmitis, following penetration of the cornea by urticating hairs.
Consumptive coagulopathy with secondary fibrinolysis occurs most commonly following stings by the South American Lonomia caterpillar whose venom activates factor X and prothrombin. Patients can demonstrate bleeding from almost any anatomic site and may develop acute (and possibly chronic) renal failure.
Caterpillar venoms are produced by glandular cells in the epithelium and are stored in and injected by urticating hairs and spines (setae). Some species produce toxic hemolymph, which can cause human disease.
In some patients, immunoglobulin E (IgE) antibodies are produced following contact, resulting in a hypersensitive state and the production of generalized urticaria on subsequent re-contact. A few caterpillars lacking urticating hairs are capable of inducing a contact dermatitis (type IV hypersensitivity).
Some caterpillars and moths release their toxic hairs into the environment, where the hairs can be inhaled. Pets or contaminated objects also can carry venomous hairs. In any of these situations, contact with the hairs can cause rhinitis or respiratory disease. Seasonal epidemics of respiratory disease have occurred in Latin America because of this phenomenon. The pathologic response leading to erucism or lepidopterism consists of acute inflammation and cellular infiltration around hairs that have penetrated the skin or conjunctiva or have been inhaled into the respiratory tract.
In the skin, diffuse vascular dilatation occurs, with subsequent edema formation in the superficial dermis and ballooning of keratinocytes within the epidermis that can lead to vesiculation. In the eye, hairs have a remarkable penetrating capacity and may work their way into the cornea, anterior chamber, or lens, where an intense inflammatory response occurs secondary to the nature of the foreign material and direct toxic effects.
Caterpillar venom-filled spines, found only in the larval forms (adult moths and butterflies do not sting), are hollow structures with a single basal poison cell that produces toxin. When pressed into human skin, the tip of the spine fractures, and the venom is injected under pressure. Toxicity declines significantly after the creature's death, but irritant or toxic hairs may retain the ability to cause dermatitis for years. Likewise, the toxic hemolymph of some caterpillars retains its potency for prolonged periods after the animal's death.
Caterpillar venoms are poorly studied but may contain peptides, hyaluronidase, phospholipase A, and biogenic amines such as histamine or histamine-releasing substances. Some, such as the South American Lonomia species, contain fibrinolytic proteases and coagulation activators that can stimulate a consumptive coagulopathy and renal failure in victims.
Although no accurate information is available, epidemics of erucism and lepidopterism have been reported. These include school closings, outbreaks of dermatitis and rhinitis in the thousands, and symptoms in more than 500,000 people caused by airborne caterpillar hair dispersion.
International
No accurate information is available, though it appears that the incidence of human disease is increasing.
Age
Children, being prone to want to play with caterpillars, may be at increased risk of exposure.
Occasional case reports of death from erucism exist, but death is very rare following stings by most species. Death may be secondary to a hypersensitivity reaction or bleeding diathesis in cases involving caterpillars of the Saturniidae family. In this family, South American Lonomia caterpillars have a high fatality rate (approximately 1.7%) due to the toxicity of their venoms and the fact that many exposures lead to multiple stings due to the communal nature of these species. No deaths have been reported following M opercularis stings.
Reported complications include panophthalmitis, consumptive coagulopathy, intracranial hemorrhage, renal failure, and osteochondritis.
While the history of exposure related temporally to the onset of signs and symptoms may be clear, the diagnosis can be challenging. Maintain a high index of suspicion when patients present with unexplained acute dermatitis, rhinitis, conjunctivitis, or wheezing during months when caterpillars are numerous. In some regions of the world, the diagnosis becomes clear when clusters of seemingly unrelated cases start to present.
Onset of acute dermatitis due to hair exposure may immediately follow exposure or may be delayed 8-12 hours.
Intense pruritus, local pain or soreness (less common), and erythematous raised rash, blisters, and bruising at the site may occur.[1, 2] Skin necrosis has occurred following prolonged exposure to toxic hairs. With most toxic caterpillars, systemic symptoms are unusual in the absence of respiratory exposure.
Respiratory exposure may precipitate acute rhinitis, tearing, cough, dyspnea, respiratory distress, wheezing, and chest pain. This syndrome may need to be differentiated from the rare case of anaphylaxis.
Ocular exposure may initiate an acute conjunctivitis with severe pain, tearing, and redness. Visual acuity can be reduced as inflammation progresses.
Stings by venomous caterpillars result in immediate, localized, severe, burning pain, which can radiate proximally and be severe enough to inhibit movement of the extremity (pseudoparalysis). Redness and swelling with slight bruising may occur at the site. Over the first few days, the patient may note the development of small blisters, which can become hemorrhagic. Local findings, including pain, may persist for several days.
Systemic complaints may occur within minutes of the sting, although they usually occur within 2 hours. These complaints include headache, dizziness, restlessness, nausea and vomiting, malaise, swollen or tender lymph nodes, muscle spasms, rapid heart rate, and, in exceptional cases, altered mental status. Systemic symptoms usually resolve in 24 hours.
Following stings by some of the New World caterpillars in the family Saturniidae, which contain a fibrinolytic component to their venoms, patients may note scattered bruising (onset in 8-72 h) and bleeding from any of a number of sites (eg, gingival bleeding, hematuria). Intracranial bleeding and acute renal failure (rarely chronic renal failure) are possible complications. Coagulopathy can last 2-5 weeks.
Local findings include erythematous papules that tend to congregate around the face, neck, trunk, arms, wrists, and hands and may become confluent; vesicles; local purpura; or ecchymosis.
Systemic signs may include a low-grade fever.[3] Anaphylaxis is reported.[4]
Findings of respiratory exposure include acute rhinitis, tearing, respiratory distress, and wheezing.
Ocular exposure can result in acute conjunctivitis. Following penetration of the cornea, findings include keratitis,[5] acute uveitis, ophthalmia nodosa,[6] and retinochoroiditis.
Local findings from stings can include erythema, edema, small petechiae or hemorrhagic papules, vesicles, bullae, and pseudoparalysis of the extremity because of pain. Following M opercularis stings, the site may take on a gridlike pattern matching the distribution of the creature's spines.
Systemic findings from stings can include restlessness, lymphangitis, oropharyngeal edema, lymphadenopathy, muscle spasms, tachycardia, altered mental status (unusual), seizures, and hypotension.[7, 8]
The wounds or dermatitis that follow exposures to irritant or toxic caterpillars and moths can become secondarily infected, which can lead to scarring and permanent dysfunction. The risk is increased when hairs or spines are retained or in patients with severe pruritus that leads to excessive scratching. In rare cases, necrosis can result from prolonged exposure to caterpillar or moth setae.
Ocular exposures can cause development of keratitis, acute uveitis, retinochoroiditis, endophthalmitis, and ophthalmia nodosa in the setting of retained hairs that tend to migrate into the eye. The ultimate outcome may be permanent blindness.
An uncommon but very concerning complication following caterpillar or moth exposures is the development of anaphylaxis in sensitized individuals.
Following stings by some of the New World caterpillars in the family Saturniidae, which contain a fibrinolytic component to their venoms, patients may note scattered bruising (onset in 8-72 h) and bleeding from any of a number of sites (eg, gingival bleeding, hematuria).[9, 10, 11] Intracranial bleeding and acute renal failure (rarely chronic renal failure) are possible complications.[12] Coagulopathy can last 2-5 weeks.
Laboratory studies are generally not required for caterpillar stings unless evidence of coagulopathy is present, as in some New World caterpillars in the family Saturniidae (Lonomia species). Those that may be warranted include the following:
CBC count
Coagulation studies: Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen level, fibrin degradation products, D-dimer assay, urine bedside test for blood
The involved skin should be immediately washed with soap and water, and dried without contacting the skin (eg, use a hair dryer).
Local cooling measures can be applied to reduce pain. This may be enhanced by applying topical isopropyl alcohol or ammonia.
Following ocular exposure, the eyes should be irrigated immediately with copious water.
Following dermal exposure to irritant or toxic hairs or setae of caterpillars or moths, sticky tape (especially duct tape) can be applied to the site in an effort to remove retained setae. Alternative effective methods of removal include use of rubber cement, clear fingernail polish, or facial peels (each applied, allowed to dry, then peeled away).
If acute symptoms follow respiratory exposure, supportive care is in order as necessary, including oxygen, antihistamines, and beta-agonist inhalers, if available.
Anaphylaxis should be treated in standard fashion.
Following caterpillar stings, the extremity should be splinted and elevated, and ice should be applied to reduce pain.
Any potentially constrictive jewelry should be removed before swelling progresses.
Wash the skin with soap and water as mentioned above if this has not already been done in the field.
Ensure appropriate tetanus immunization status.
Skin exposure
Apply sticky adhesive tape (especially duct tape) to the site to remove all remaining hairs or spines possible. Other measures of removal as described previously for prehospital care can also be tried.
Acute dermatitis can be treated with antihistamines (H1 and/or H2 blockers), although their efficacy is controversial. Additionally, topical steroids may be employed. Systemic steroids may be necessary in patients with severe or persistent cutaneous symptoms. Application of antipruritic products containing menthol may be soothing.
Prostaglandin-synthetase inhibitors, such as aspirin or indomethacin, have been reported to reduce associated discomfort, but should be avoided if any evidence of coagulopathy is present.
Respiratory exposure
Symptoms can be managed with antihistamines (H1 and/or H2 blockers) and beta agonist aerosols/inhalers if wheezing is present.
If significant symptoms occur, supplemental oxygen administration may be needed, and systemic steroids may be useful.
Ocular exposure
Instill a topical anesthetic and irrigate the eyes immediately with copious saline.
Perform a slit lamp examination with fluorescein. The patient should receive close ophthalmologic follow-up care to rule out retained setae or hairs.
Eye complications resulting from retained migrating hairs/setae can be severe, and surgical excision may be necessary.
Stings
Management is primarily symptomatic and supportive. Splint and elevate the involved extremity; ice can be applied to reduce pain and swelling. Efforts, as outlined above, should be instituted to remove any retained spines or hairs.
Narcotic analgesics may be required for pain relief. Anecdotal reports exist of the successful use of calcium gluconate (eg, 10 mL of a 10% solution by slow intravenous [IV] administration) to relieve muscle pain following M opercularis stings. Antihistamines (H1 and/or H2 blockers) may reduce concomitant pruritus.
Anaphylaxis
Treat rare cases of caterpillar or moth-related anaphylaxis in standard, aggressive fashion, including airway management, epinephrine, oxygen, antihistamines, steroids, IV fluids, and vasopressors as needed.
Consultations usually are not necessary following most caterpillar contacts. An ophthalmologist should be promptly consulted if ocular involvement is present.[13] Repeated ophthalmologic intervention to remove embedded hairs may be necessary.[14]
All caterpillars should be considered potentially toxic, and contact should be avoided. Children particularly should be warned in this regard. When working outdoors during peak caterpillar seasons, individuals should wear long-sleeved shirts, long pants with the cuffs tucked into their socks, and work gloves. Collars should be close fitting to avoid having a caterpillar fall into one's shirt. A broad-brimmed hat may prevent caterpillars from falling from an overhead tree onto one's head and face. When working in an area where airborne caterpillar debris is a problem, a tight-fitting face mask and eye protection should be used. Laundered clothing should not be hung outdoors to dry as it may collect airborne caterpillar debris.
Insecticides can be used to control caterpillar populations. A professional pest specialist or entomologist should be consulted before applying such agents because many caterpillar species are beneficial to agricultural and ornamental plants.
If a caterpillar is found on one's body, it should be gently lifted off with a stick to avoid contact with potentially toxic hairs, setae, or hemolymph.
Victims of caterpillar stings can be observed for 2 hours in the ED to ensure that they do not develop significant systemic toxicity.
Although uncommon, secondary infection can occur following erucism or lepidopterism. Instruct patients to follow up immediately if any signs or symptoms of infection occur. Patients with particularly severe exposures should have scheduled follow-up care to exclude infection or necrosis.
All patients with ocular exposures to caterpillar or moth hairs or setae should receive early ophthalmologic follow-up care to exclude retained fragments, which can lead to catastrophic complications.
Following caterpillar stings, local findings, including pain, may persist for several days. Systemic symptoms usually resolve in 24 hours.
Patients who experience a significant allergic reaction to caterpillar exposure (eg, hypotension, bronchospasm) should receive a prescription for an epinephrine self-administration device prior to discharge from the hospital and should be instructed in its use. They also should consider obtaining and carrying medical alert identification of this history. Unlike therapy for hymenoptera-induced anaphylaxis, there is no desensitization therapy for patients highly allergic to caterpillars.
Epinephrine and systemic antihistamines (eg, diphenhydramine, cimetidine), topical or systemic steroids, menthol-containing creams, and prostaglandin-synthetase inhibitors, such as aspirin and indomethacin, all may be beneficial in treating dermatitis. Rhinitis resulting from respiratory exposure may respond to antihistamines and systemic steroids. These are also useful for lower respiratory symptoms. Beta-agonist aerosols or inhalers (eg, albuterol) may be beneficial for wheezing. Analgesics may be required for caterpillar stings. The choice of agent should depend on the severity of symptoms. Mild cases may be treated adequately with oral opiates such as hydrocodone or oxycodone, while more severe pain initially may require parenteral agents such as morphine sulfate.
Stings by the South American Lonomia species, which can cause consumptive coagulopathy with hemorrhagic diathesis and acute renal failure, may be treated with antifibrinolytics. If blood products are required, they must be given cautiously to avoid feeding fuel to an on-going consumptive coagulopathy. An antivenom against this species has been produced in Brazil.[15]
Clinical Context:
Cimetidine is an H2 antagonist that, when combined with an H1 type, may be useful in treating itching and flushing in anaphylaxis, pruritus, urticaria, and contact dermatitis that do not respond to H1-receptor antagonists alone. Use it in addition to H1 antihistamines.
Antihistamines prevent histamine response in sensory nerve endings and blood vessels. They are more effective in preventing a histamine response than in reversing it.
Clinical Context:
Methylprednisolone decreases inflammation by suppressing the migration of polymorphonuclear leukocytes and reversing increased capillary permeability.
Clinical Context:
Prednisone decreases inflammation by suppressing the migration of polymorphonuclear leukocytes and reversing increased capillary permeability.
Clinical Context:
Topical hydrocortisone is the drug of choice for reducing cutaneous inflammatory responses in caterpillar-induced dermatitis. It is an adrenocorticosteroid derivative suitable for application to skin or external mucous membranes. It has mineralocorticoid and glucocorticoid effects, resulting in anti-inflammatory activity.
Their onset of action is approximately 4-6 hours, and they have limited benefit in the initial acute treatment of rapidly deteriorating anaphylactic patients. However, corticosteroids may benefit patients with persistent bronchospasm or hypotension.
Topical steroids can help reduce the cutaneous inflammatory response in caterpillar-induced dermatitis.
Clinical Context:
Albuterol is a beta-agonist useful in the treatment of bronchospasm refractory to epinephrine. It relaxes bronchial smooth muscle by acting on beta2 receptors with little effect on the heart rate.
Clinical Context:
Alpha-agonist effects increase peripheral vascular resistance and reverse peripheral vasodilatation, vascular permeability, and systemic hypotension. Conversely, beta-agonist effects produce bronchodilatation, cause positive inotropic and chronotropic cardiac activity, and result in an increased production of intracellular cAMP.
Clinical Context:
Ipratropium bromide is a synthetic quaternary anticholinergic ammonium compound chemically related to atropine; it has antisecretory properties; when applied locally, it inhibits secretions from serous and seromucous glands lining nasal mucosa.
Via combined alpha-adrenergic and beta-adrenergic agonist action, sympathomimetics are effective in reversing acute bronchospasm of allergic or irritant origin.
An additional option in the management of persistent bronchospasm is via anticholinergics. These agents block the action of acetylcholine at parasympathetic sites in bronchial smooth muscle, causing bronchodilation.
Pain control is essential to quality patient care. Most analgesics have sedating properties, which may be beneficial for patients who have sustained severe caterpillar stings.
Clinical Context:
Indomethacin is a commonly prescribed NSAID used for reducing inflammatory responses. It is rapidly absorbed; metabolism occurs in the liver by demethylation, deacetylation, and glucuronide conjugation; it inhibits prostaglandin synthesis.
Clinical Context:
Dopamine may be required to support blood pressure in the face of hypotension caused by anaphylactic/anaphylactoid reaction that is unresponsive to fluids and epinephrine.
Clinical Context:
Tetanus toxoid adsorbed or fluid is used to induce active immunity against tetanus in selected patients. The immunizing agent of choice for most adults and children older than 7 years are tetanus and diphtheria toxoids. It is necessary to administer booster doses to maintain tetanus immunity throughout life.
Pregnant patients should receive only tetanus toxoid, not a diphtheria antigen-containing product.
In children and adults, it may be administered into the deltoid or midlateral thigh muscles. In infants, the preferred site of administration is mid thigh laterally.
These are used for tetanus immunization. A booster injection in previously immunized individuals is recommended to prevent this potentially lethal syndrome.
Robert L Norris, MD, Professor Emeritus, Department of Emergency Medicine, Stanford University Medical Center
Disclosure: Nothing to disclose.
Specialty Editors
John T VanDeVoort, PharmD, Regional Director of Pharmacy, Sacred Heart and St Joseph's Hospitals
Disclosure: Nothing to disclose.
Gino A Farina, MD, FACEP, FAAEM, Professor of Emergency Medicine, Hofstra North Shore-LIJ School of Medicine at Hofstra University; Program Director, Department of Emergency Medicine, Long Island Jewish Medical Center
Disclosure: Nothing to disclose.
Chief Editor
Joe Alcock, MD, MS, Associate Professor, Department of Emergency Medicine, University of New Mexico Health Sciences Center
Disclosure: Nothing to disclose.
Additional Contributors
Samuel M Keim, MD, MS, Professor and Chair, Department of Emergency Medicine, University of Arizona College of Medicine
Caterpillar envenomations. Puss caterpillar or asp. Photo courtesy of the Arizona Poison and Drug Information Center.
Caterpillar envenomations. Puss caterpillar or asp. Photo courtesy of the Arizona Poison and Drug Information Center.
Distinguishing dangerous from harmless caterpillars can be difficult, and handling any caterpillar with bare skin should be avoided. These are harmless tomato hornworm caterpillars (larval form of the five-spotted hawk moth [Manduca quinquemaculata])
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