— This article by Jerry Cates, first published on 7 March 2010, was last revised on 22 January 2014. © Bugsinthenews Vol. 11:03(09).
The puss caterpillar is the larva of an insect in the order Lepidoptera.
More specifically, it is a flannel moth (so-called because the adult moth is clothed in short fine hairs that resemble flannel in texture) in the family Megalopygidae: from the Greek root μεγας (MEG-as) = great, vast, large + the Greek root πυγη (PIDGE-ee) = rump, tail + the Greek patronymic suffix –ιδες (eye-DEES) commonly used in zoological taxonomy to indicate a family name, in reference to a family of moths typically having an exaggerated tail, honoring the fact that these caterpillars often–but not always–trail a conspicuous tail of hairs; this family is presently represented by 23 recognized genera that are found in North America and in the New World Tropics; in North America as many as 44 species — generally described as that group of organisms capable of interbreeding and producing fertile offspring — have been described, some of which may be synonyms, but all of which are known, while in the larval (caterpillar) stage, to produce extremely painful stings in humans who come into contact with them.
The species cited most often is Megalopyge opercularis, but a number of other species present a similar outer guise, are equipped with near-identical envenomating structures, and produce a similar sting on contact with human skin.
Most are now considered to be members of the genus Megalopyge , but the crinkled flannel moth–also known as the black-waved flannel moth–is classified by some authorities as a member of the genus Lagoa (Lagoa crispata), and by others as Megalopyge crispata.
In the material that follows, because the gross features of most, if not all of these moths are essentially identical, no attempt will be made to distinguish between them.
The larval stage of this insect is a small (2 cm. long, 1 cm. wide), woolly, pussycat-appearing caterpillar.
Its innocent, cuddly-looking appearance belies the numerous sharp, venom-laden spines, hidden beneath its luxuriant coat of soft hairs.
Because these caterpillars appear as innocuous pieces of fluff, children and adults are tempted to pick them up.
Even those who know their nasty reputations find it difficult to believe that these beautifully adorned animals — that have all the earmarks of a benign, friendly, comforting creature —have the power to move powerful, grown men to tears of pain and agony.
One touch, however, quells all doubts in a blinding instant of truth. Talk about pain… Wow! The puss caterpillar knows how to dish it out most of the time (some, thankfully, don’t sting, probably because a chance genetic mutation prevents their bodies from manufacturing the venom that otherwise fills their spines).
The spines that stick out from each verruca (a Latin word meaning “wart”; in this case a glandular excrescence on the skin of the caterpillar that houses venom glands and is adorned dorsally with sharp, hollow, venomous spines) on the body of the caterpillar usually , but not always, induce an immediate onset of excruciating, unrelenting pain.
The pain usually radiates rapidly to the lymph nodes in the armpit or groin, and then to the chest.
Though only rarely representing a true medical emergency, these symptoms have the feel of a genuine, serious, life-threatening event.
As a result, it is common for victims of puss caterpillar stings to seek medical assistance at hospital emergency rooms, where they hope that the E.R. staff will be able to apply appropriate medical interventions.
Sometimes Emergency Room physicians, nurses, and EMTs recognize the puss caterpillar’s distinctive sting wound immediately, but — surprisingly often — these personnel have no knowledge of the puss caterpillar or its sting, much less of the most effective medical interventions the sting calls for.
Individuals who go to emergency rooms for treatment of puss caterpillar stings may be misdiagnosed by inexperienced medical personnel as suffering from a wide range of acute and generally serious medical conditions.
Within minutes or hours of the sting event, a halo of reddened skin, caused by capillary congestion, forms. The reddened tissue is locally sensitive, painful, and warm or hot to the touch.
The skin remains reddened but otherwise unmarked for minutes or hours. As the local redness subsides, a pattern of darker, raised, nodular lesions forms, usually within 24 hours after the sting. These darker lesions are arranged in a characteristic pattern.
The sting pattern varies based on which portion of the caterpillar touches the body.
The puss caterpillar’s underside is shown in the photo at right. This portion of the caterpillar contacts the surface of the caterpillar’s track as the caterpillar crawls along. Note the way the hairs along the edges of the body emerge from swollen “warts” or verrucae (raised tubercular ridges, arranged along the median of each body segment).
Though the soft hairs themselves are harmless, these same swellings also sport a multitude of sharp, venomous spines capable of injecting the caterpillar’s venom into the skin of a sting victim. If the underside is pressed against the body, the visible sting pattern (that shows up later) will follow this shape; if one side of the caterpillar is involved, the sting pattern is usually that of a crosshatched triangle, with each of the verrucae involved in the sting showing in the pattern. If the upper surface is pressed against the skin, the sting pattern is that of a crosshatched oval.
The sting pattern usually begins to show within 24 hours, but the full pattern may not be expressed for hours or days after the sting occurs.
The photos below show puss caterpillar stings on a right foot foot (L) and forearm (R). The lateral (side) surface of a caterpillar had been crushed against the foot, while the stings on the forearm were caused when the upper bodies of two caterpillars were crushed by pressing the arm against a railing where the caterpillars were crawling. Note the regular pattern of dark red spots in the photos; these spots correspond to the verrucae in the body of the caterpillar, showing where the concentrations of fragile, venomous spines penetrated the sting victim’s skin. In the majority of cases, these spines break off during penetration and slowly release their store of venom as long as they remain embedded. Each spine, as described by Nathan C. Foot in his 1921 paper on the subject, is one-third to one milimeter long, and 15-45 microns in diameter. Such microscopic structures cannot be seen with the naked eye. However, because human flesh tends to push embedded foreign objects outward, even spines that have penetrated deeply will move toward the surface of the skin–where they may be extracted manually–within a relatively short time. This fact figures prominently in the treatment options that should be considered when dealing with a puss caterpillar sting.
These photos were taken several hours after the sting event.
Links: (1) Puss Caterpillar General Information. (2) The Puss Caterpillar’s Stinging Apparatus. (3) Puss Caterpillar Extermination. (4) The Puss Caterpillar’s Natural Predators. (5). Puss Caterpillar Stings–Medical Interventions. (6) Puss Caterpillar Stings–Home Remedy First Aid Measures.
- Kingdom Animalia (ahn-uh-MAYHL-yuh) — first described in 1758 by the Swedish taxonomist Carolus Linnaeus (1707 – 1778), using the Latin word animal = “a living being,” from the Latin word anima = “vital breath”, to refer to multicellular, eukaryotic organisms whose body plans become fixed during development, some of which undergo additional processes of metamorphosis later in their lives; most of which are motile, and thus exhibit spontaneous and independent movements; and all of whom are heterotrophs that feed by ingesting other organisms or their products;
- Phylum Arthropoda (ahr-THROPP-uh-duh) — first described in 1829 by the French zoologist Pierre André Latreille [November 20, 1762 – February 6, 1833], using the two Greek roots αρθρον (AR-thrawn) = jointed + ποδ (pawd) = foot, in an obvious reference to animals with jointed feet, but in the more narrow context of the invertebrates, which have segmented bodies as well as jointed appendages;
- Class Insecta (ehn-SEK-tuh) — first described in 1758 by the Swedish taxonomist Carolus Linnaeus (1707 – 1778), using the Latin word insectum, a calque of the Greek word ἔντομον ( EN-toh-mawn) = “(that which is) cut into sections”; comprised of arthropods with chitinous external (exo-) skeletons, a three part body composed of a distinct head, thorax, and abdomen, the midmost part having three pairs of jointed legs, and the foremost part having a pair of compound eyes and antennae;
- Subclass Pterygota (tare-ee-GOH-tah) — first described in 1888 by Lang, using the Greek roots πτερυξ (TARE-oos) = wing, to refer to insects with wings, or that had wings but in the process of evolution have since lost them;
- Infraclass Neoptera (nee-OPP-tur-uh) — first described in 1890 by the Dutch entomologist Frederick Maurits van der Wulp (1818-1899) using the Greek roots νεος (NEE-ose) = youthful, new + πτερυ (TARE-ohn) = wing, to refer to winged insects that are capable of folding their wings over their abdomens, in contrast to more primitive winged insects that are unable to flex their wings in this manner (e.g., the dragonflies, in the infraclass Paleoptera);
- Superorder Endopterygota (ehn-doh-tare-ee-GOH-tah) — first described by the English physician and entomologist David Sharp (1840-1922) using the Greek root ενδον (ENN-dohn) = within + the established expression pterygota (see above) to refer to insects within the latter subclass that undergo complete metamorphosis, i.e., larval, pupal, and adult stages;
- Order Lepidoptera (lep-uh-DOPP-tur-uh) — first formally described in 1758 (though he coined the expression in 1735, informally) by the Swedish taxonomist Carolus Linnaeus (1707 – 1778), using the Greek roots λεπιδωτος (lepp-eh-DOH-tose) = scaly + πτερυ (TARE-ohn) = wing, to refer to insects with scales covering their wings, i.e., the moths and butterflies;
- Family Megalopygidae (megg-uh-low-PIDGE-uh-dee) — from the Greek root μεγας (MEG-as) = great, vast, large + the Greek root πυγη (PIDGE-ee) = rump, tail + the Greek patronymic suffix -ιδες (eye-DEES) commonly used in zoological taxonomy to indicate a family name, in reference to a family of moths typically having an exaggerated tail, honoring the fact that these caterpillars often–but not always–trail a conspicuous tail of hairs; this family is presently represented by 23 recognized genera that are found in North America and in the New World Tropics; in North America as many as 44 species have been described, some of which may be synonyms, but all of which are known, while in the larval (caterpillar) stage, to produce extremely painful stings in humans who come into contact with them;
- Avilán, Luisana, et al. 2010. Description of envenomation by the “gusano-pollo” caterpillar (Megalopyge opercularis) in Venezuela. Invest Clin 51(1): 127 – 132.
- Bennett, Gary W. 2010. Truman’s Scientific Guide to Pest Management Operations 7th Edition. Purdue University.
- Borror, Donald J., and Richard E. White. 1970. A Field Guide to Insects: America North of Mexico. Houghton Mifflin Company
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- Epstein, Marc E. 1995. Evolution of locomotion in slug caterpillars (Lepidoptera: Zygaenoidea: Limacodid group). J. Res. Lepidoptera 34:1-13.
- Foot, Nathan Chandler. 1922. Pathology of the Dermatitis caused by Megalopyge opercularis, a Texan caterpillar. JEM 35(5): 1 May 1922.
- Khalaf, Kamel T. 1974. Nonasceptic Wheat Germ Diet for Megalopyge opercularis (Lepidoptera: Megalopygidae). The Florida Entomologist 57(4):377-381.
- Klotz, John H. et al. 2009. Animal Bites and Stings with Anaphylactic Potential. J. Emerg. Med. 36(2):148-156.
- Lifton, Bernice. 2005. Bug Busters: Poison-Free Pest Controls for Your House and Garden. Square One Publishers.
- Mallis, Arnold, Stoy Hedges (Ed.) et al. 2011. The Mallis Handbook of Pest Control, 10th Edition. The Mallis Handbook Company.
- Neck, Raymond W. 1976. Lepidopteran Foodplant Records from Texas. J. Res. Lepidoptera 15(2):75-82.
- Steen. Christopher J. et al. Arthropods in dermatology. J. Am. Dermatol. 50(6):819-842.
- Stewart, Amy. 2011. Wicked Bugs: The Louse That Conquered Napoleon’s Army & Other Diabolical Insects. Algonquin Books of Chapel Hill.
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