Megalopyge opercularis

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Megalopyge opercularis
Megalopyge opercularisPCCP20040714-5799B.jpg
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Lepidoptera
Family: Megalopygidae
Genus: Megalopyge
Species: M. opercularis
Binomial name
Megalopyge opercularis
(JE Smith, 1797)

Megalopyge opercularis is a moth of the family Megalopygidae. It has numerous common names, including southern flannel moth for its adult form, and puss moth, puss caterpillar, tree asp, and the asp caterpillar for its larval form.


M. opercularis is visually striking in both larval and adult forms.


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 the larva a cottony, puffed-up look. The body tapers to a tail that extends well beyond the body, unlike its relative M. crispata.[1] 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 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.[2] Additionally, it is not unusual to find sweating from the welts or hives at the site of the sting. Ironically, the resemblance of the larvae to soft, colorful cotton balls encourages people to pick them up and pet them.


The adult moth is covered in long fur in colors ranging from dull orange to lemon yellow, with hairy legs and fuzzy black feet.


A M. opercularis caterpillar on Kent Island, Maryland.

M. opercularis can be found on oaks, elms, citrus and other trees, and many garden plants such as roses and ivy. It is distributed throughout the eastern United States between North Carolina and Florida, the southern United States, Mexico, and parts of Central America. The larva does not spin a real cocoon; rather, it separates from its furry skin and uses it as a protective covering while it pupates.

Dangers and treatment of stings[edit]

Exposure to the caterpillar's fur-like spines will lead to an immediate skin irritation. The caterpillar is regarded as a dangerous insect because of its venomous spines. Medical advice may be sought in case of contact with one. It is best if the venom from the spines is treated within hours of first contact. For first aid, it is recommended that the spines (if present) be removed by using cellophane tape.[2]

Other 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, or calamine lotion.[2] It is not recommended to rub wounds or apply alcohol, spirits, ammonia, or urine, as these can encourage the release of additional venom and may have strongly negative effects.[3]


  1. ^ Wagner, DL (2005), Caterpillars of Eastern North America., Princeton Univ. Press 
  2. ^ a b c Eagleman, DM (2007). "A Study of the Geographical Distribution and Symptoms of Envenomation by the Asp Caterpillar, Megalopyge opercularis" (PDF). Clinical Toxicology. 46 (3): 201–5. doi:10.1080/15563650701227729. 
  3. ^ Hartwick R, Callanan V, Williamson J (1980). "Disarming the box-jellyfish: nematocyst inhibition in Chironex fleckeri". Med J Aust. 1 (1): 15–20. PMID 6102347. 

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