Megalopyge opercularis

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Megalopyge opercularis
Megalopyge opercularisPCCP20040714-5799B.jpg
Asp Caterpillar.jpg
Scientific classification edit
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Lepidoptera
Family: Megalopygidae
Genus: Megalopyge
M. opercularis
Binomial name
Megalopyge opercularis
(JE Smith, 1797)
Synonyms[citation needed]
  • Phalaena opercularis Smith, 1797[1][2]
  • Megalopyge albizona Dognin, 1923
  • Megalopyge bissesa Dyar, 1910
  • Megalopyge briseis Dyar, 1910
  • Megalopyge costaricensis Schaus, 1912
  • Megalopyge govana Schaus, 1904
  • Megalopyge incachaca Schaus, 1927
  • Pimela lanuginosa Clemens, 1860
  • Lagoa ornata Druce, 1887

Megalopyge opercularis is a moth of the family Megalopygidae. It has numerous common names, including southern flannel moth for its adult form, and puss caterpillar, asp, Italian asp, fire caterpillar, woolly slug, opossum bug,[3] puss moth, tree asp, or asp caterpillar.


M. opercularis caterpillar on Kent Island, Maryland

The inch-long larva is generously coated in long, luxuriant hair-like setae, making it resemble a tiny Persian cat, the characteristic that presumably gave it the name "puss". It is variable in color, from downy grayish white to golden brown to dark charcoal gray. It often has a streak of bright orange running longitudinally. The "fur" on early-stage larvae is sometimes extremely curly, giving them a cottony, puffed-up look. The body tapers to a tail that extends well beyond the body, unlike its relative M. crispata.[4] The middle instar has a more disheveled, "bad-hair-day" appearance, without a distinctive tail. The "fur" of the larva contains venomous spines that cause extremely painful reactions in human skin upon contact. The adult moth is covered in long fur in colors ranging from dull orange to lemon yellow, with hairy legs and fuzzy black feet.


M. opercularis can be found on oak, elm, and wild plum, among others, as well as many garden plants such as roses and ivy. It is distributed throughout the Eastern United States between extreme southeastern Virginia and Florida across the south to Texas, Mexico, and parts of Central America. The caterpillar has 2 broods, one in the summer and the other in the fall. Late larvae may stay in their cocoon all winter, and emerge in late spring as an adult. [5]

Dangers and treatment of stings[edit]

The caterpillar is regarded as a dangerous insect because of its venomous spines. Exposure to the caterpillar's fur-like spines leads to an immediate skin irritation characterized by a "grid-like hemorrhagic papular eruption with severe radiating pain." Victims describe the pain as similar to a broken bone or blunt-force trauma,[3] or even white hot.[6] The reactions are sometimes localized to the affected area, but are often very severe, radiating up a limb and causing burning, swelling, nausea, headache, abdominal distress, rashes, blisters, and sometimes chest pain, numbness, or difficulty breathing.[7][8] Sweating from the welts or hives at the site of the sting is not unusual.[9]

The venom from the spines is best treated within hours of first contact. For first aid, the spines (if present) should be removed by using cellophane tape.[7] Some remedies, which are reported to have varying degrees of success, include ice packs, oral antihistamine, baking soda, hydrocortisone cream, juice from the stems of comfrey plants, and calamine lotion.[7]


  1. ^ Smith, James Edward (1797). "Tab. LIII. Phalæna opercularis". The Natural History of the Rarer Lepidopterous Insects of Georgia. Including their systematic characters, the particulars of their several metamorphoses, and the plants on which they feed. Collected from the observation of Mr. John Abbot, many years resident in that country. Vol. 2. London: T. Bensley. pp. 105–106.
  2. ^ Simmons, Alvin M.; Wiseman, B. R. (1993). "James Edward Smith - Taxonomic Author of the Fall Armyworm". The Florida Entomologist. 76 (2): 275. doi:10.2307/3495726. JSTOR 3495726.
  3. ^ a b Hossler, Eric W. (2009). "Caterpillars and moths". Dermatologic Therapy. 22 (4): 353–366. doi:10.1111/j.1529-8019.2009.01247.x. PMID 19580579. S2CID 31799282.
  4. ^ Wagner, David L. (2005). "Flannel Moths – Megalopygidae". Caterpillars of Eastern North America. Princeton Univ. Press. p. 55. ISBN 1400834147.
  5. ^ McGovern, John P.; Barkin, Gilbert D.; McElhenney, Thomas R.; Wende, Reubin (1961). "Megalopyge opercularis: Observations of Its Life History, Natural History of Its Sting in Man, and Report of an Epidemic". JAMA. 175 (13): 1155–1158. doi:10.1001/jama.1961.03040130039009.
  6. ^ "Venomous caterpillar 'no one has heard of' sends New Kent woman to ER".
  7. ^ a b c Eagleman, David M. (2007). "Envenomation by the asp caterpillar (Megalopyge opercularis)". Clinical Toxicology. 46 (3): 201–205. doi:10.1080/15563650701227729. PMID 18344102. S2CID 15696836.
  8. ^ Demkovich, Laurel (June 20, 2018). "'BE AWARE': Pasco mom posts to Facebook after son's caterpillar sting leads to ER trip". Tampa Bay Times. Retrieved 2018-06-21.
  9. ^ Eagleman, David M. (January 2008). "Envenomation by the asp caterpillar ( Megalopyge opercularis )". Clinical Toxicology. 46 (3): 201–205. doi:10.1080/15563650701227729. ISSN 1556-3650. PMID 18344102. S2CID 15696836.

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