Pyrrharctia isabella

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Isabella tiger moth
Pyrrharctia isabella – Isabella Tiger Moth (14842796231).jpg
Pyrrharctia isabella - Caterpillar - Devonian Fossil Gorge - Iowa City - 2014-10-15 - image 1.jpg
Woollybear caterpillar
Scientific classification edit
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Lepidoptera
Superfamily: Noctuoidea
Family: Erebidae
Genus: Pyrrharctia
P. isabella
Binomial name
Pyrrharctia isabella
(J. E. Smith, 1797)
  • Phalaena isabella J. E. Smith, 1797
  • Pyrrharctia californica Packard, 1864

Pyrrharctia isabella, the isabella tiger moth, banded woolly bear or just woollybear or woolly worm, occurs in the United States and southern Canada.[1][2][3][4] The first European to describe it was James Edward Smith in 1797.


The thirteen-segment larvae are usually covered with brown hair in their mid-regions and black hair in their anterior and posterior areas. In direct sunlight, the brown hair looks bright reddish brown. Adults are generally dull yellowish through orangish and have robust, scaly thorices; small heads; and bright reddish-orange forelegs. Wings have sparse black spotting.[citation needed]

The isabella tiger moth can be found in many cold regions, including the Arctic. The banded woolly bear larva emerges from the egg in the fall and overwinters in its caterpillar form, when it literally freezes solid. First its heart stops beating, then its gut freezes, then its blood, followed by the rest of the body. It survives being frozen by producing a cryoprotectant in its tissues. [5] In the spring it thaws.

Larval setae do not inject venom and are not urticant; they do not typically cause irritation, injury, inflammation, or swelling.[6] Handling larvae is discouraged, however, because their sharp, spiny hairs may cause dermatitis in some people. When disturbed, larvae defend themselves by playing possum (rolling up into balls and remaining motionless) and quickly crawling away.[citation needed]


This species is a generalist feeder, consuming many plant species, including herbs and trees.[7]

Related species[edit]

Research[8] has shown that the larvae of a related moth, Grammia incorrupta (whose larvae are also called "woollybears"), consume alkaloid-laden leaves that help fight off internal parasitic fly larvae. This phenomenon is said to be "the first clear demonstration of self-medication among insects." Within the same family, the larvae of the garden tiger moth (Arctia caja) are also known as woollybear caterpillars and consume an alkaloid diet similar to Grammia incorrupta.

In culture[edit]


Canadian and U.S. folklore holds that the relative amounts of brown and black hair on a larva indicate the severity of the coming winter. It is believed that if a Pyrrharctia isabella's brown band is wide, winter weather will be mild, and if the brown band is narrow, the winter will be severe. In a variation of this story, the color of stripes predict the winter weather, with darker stripes indicating a harsher winter. In reality, hatchlings from the same clutch of eggs can display considerable variation in their color banding, and a larva's brown band tends to widen with age as it molts.[9]

Another version of this belief is that the direction in which a Pyrrharctia isabella crawls indicates the winter weather, with the caterpillar crawling south to escape colder weather. There is no scientific evidence for winter weather prediction by Pyrrharctia isabella.[10]

Woollybear festivals[edit]

Woollybear festivals are held in several locations in the fall.


  1. ^ "Entomology Collection > Pyrrharctia isabella". Retrieved 28 September 2018.
  2. ^ "Entomology Collection > Specimen Plot". Retrieved 28 September 2018.
  3. ^ "Isabella Tiger Moth (Pyrrharctia isabella)". Retrieved 28 September 2018.
  4. ^ "Woolly Worm Festival". Woolly Worm Festival. Retrieved 2018-10-09.
  5. ^ Layne, Jack R.; Kuharsky, Diane K. (2000). "Triggering of cryoprotectant synthesis in the woolly bear caterpillar (Pyrrharctia isabella Lepidoptera: Arctiidae)". Journal of Experimental Zoology. 286 (4): 367–371. doi:10.1002/(SICI)1097-010X(20000301)286:4<367::AID-JEZ4>3.0.CO;2-F. ISSN 1097-010X. Retrieved 2019-09-15.
  6. ^ Mullen, Gary Richard; Lance A. Durden (2002). Medical and Veterinary Entomology. Academic Press. ISBN 0-12-510451-0.
  7. ^ "Entomology Collection > Pyrrharctia isabella". E.H. Strickland Entomological Museum, University of Alberta. Retrieved 2008-11-21.
  8. ^ ""Woolly Bear Caterpillars Self-Medicate -- A Bug First" - National Geographic". Retrieved 2009-03-14.
  9. ^ Predicting Winter Weather: Woolly Bear Caterpillars, The Old Farmer's Almanac, 1999.
  10. ^ Service, US Department of Commerce, NOAA, National Weather. "Woolly Bear Caterpillar - Winter Predictor Or Not?". Retrieved 28 September 2018.
  11. ^ "Woollybear Festival »". Retrieved 28 September 2018.
  12. ^ Old Farmer's Almanac, 1999.
  13. ^ Robertson, Dan. "Oil Valley Vick & the NWPA Wooly Bear Society". Mystic Outer Rim Society. Archived from the original on 3 March 2016. Retrieved 29 March 2012. Cite uses deprecated parameter |deadurl= (help)
  14. ^ "Wooly Bear Weekend with Local Manufacturers and Artisans". Cattaraugus County. July 24, 2015. Retrieved September 28, 2018.

External links[edit]