Hyphantria cunea


Arctiidae is a large and diverse family of moths with around 11,000 species found all over the world, with 6000 Neotropical species (Scoble 1995). This family includes the groups commonly known as tiger moths (or tigers), which usually have bright colours, footmen (which are usually much drabber), lichen moths and wasp moths. Many species have 'hairy' caterpillars which are popularly known as woolly bears or woolly worms. The scientific name refers to this (Gk. αρκτος = a bear). Caterpillars may also go by the name 'tussock moths' (more usually this refers to Lymantriidae, however).


The most distinctive feature of the family is a tymbal organ on the metathorax (Scoble 1995). This organ has membranes which are vibrated to produce ultrasonic sounds. They also have thoracic tympanal organs for hearing, a trait which has a fairly broad distribution in the Lepidoptera but the location and structure is distinctive to the family. Other distinctive traits are particular setae ('hairs') on the larvae, wing venation, and a pair of glands near the ovipositor (Scoble, 1995). The sounds are used in mating (Simmons and Conner 1996) and defense against predators (Fullard et al, 1994).


Many species retain distasteful or poisonous chemicals acquired from their host plants (Weller et al., 1999). Some species also have the ability to make their own defenses (Nishida, 2002). Common defenses include: cardiac glycosides (or cardenolides), pyrrolizidine alkaloids, pyrazines and histamines (Weller et al., 1999). Larvae usually acquire these chemicals, and may retain them in the adult stage. But adults can acquire them too, by regurgitating on decomposing plants containing the compounds, and sucking up the fluid (Weller et al., 1999). Adults can transfer the defenses to their eggs, and males sometimes transfer them to females to help with defense of the eggs. Larval 'hairs' may be stinging, due to histamines the caterpillar makes in some species, but not all.

The insects advertise these defenses with aposematic bright coloration, unusual postures, odours, or, in adults, ultrasonic vibrations. Some mimic moths that are poisonous, or wasps that sting (Simmons and Weller, 2002). The ultrasound signals help nocturnal predators to learn to avoid the moths (Dunning and Roeder 1965, Hristov and Conner, 2005), and can interfere with the bat's ability to precisely locate flying moths (Ratcliffe and Fullard, 2005).

Life cycle

Many of the caterpillars and adults are active during the daytime. If disturbed, woolly bear caterpillars will roll into a tight spiral. Common folklore has it that the forthcoming severity of a winter can be predicted by the amount of black on the Isabella tiger moth's caterpillar, the most familiar woolly bear in North America; however the relative width of the black band varies among instars, not according to weather (Wagner 2005). Isabella tiger moths (Pyrrharctia isabella) overwinter in the caterpillar stage. They can survive freezing at moderate subzero temperatures by producing a cryo-protectant chemical (Layne and Kuharsky 2000). The larvae of another species, Phragmatobia fuliginosa may be found on snow seeking a place to pupate.

Although they may be abundant, few species in this family are of economic importance. Even the fall webworm, an abundant and highly polyphagous tree-feeding species that has spread from North America to Asia and Europe, does not do lasting damage to healthy hosts.


Local lore of the American Northeast holds that that "Wooly bears" have the ability to predict the weather, similar to that of the Groundhog. The lore goes: "More brown than black means a fair winter, but more black than brown means there is going to be a harsh winter". While there is no truth to this theory (the offspring of a single female can range from almost completely brown to almost completely black), they possess mythical qualities in the American Northeast, leading to such things as the Woollybear Festival.

Notable species


See also


  • Bates DL, Fenton MB (1990) Aposematism or startle? Predators learn their responses to the defenses of prey. Can J Zool 68:49–52
  • Dunning DC, Krüger M (1995) Aposematic sounds in African moths. Biotropica 27:227–231
  • Dunning DC, Roeder KD (1965) Moth sounds and the insect-catching behavior of bats. Science 147:173–174
  • Dunning DC, Acharya L, Merriman CB, Ferro LD (1992) Interactions between bats and arctiid moths. Can J Zool 70:2218–2223
  • Fullard JH, Fenton MB, Simmons JA (1979) Jamming bat echolocation: the clicks of arctiid moths. Can J Zool 57:647–649
  • Fullard JH, Simmons JA, Sailant PA (1994) Jamming bat echolocation: the dogbane tiger moth Cycnia tenera times its clicks to the terminal attack calls of the big brown bat Eptesicus fuscus. J Exp Biol 194:285–298
  • Hristov NI, Conner WE (2005) Sound strategy: acoustic aposematism in the bat–tiger moth arms race. Naturwissenschaften 92:164–169. DOI:10.1007/s00114-005-0611-7
  • Layne JR, Kuharsky DK (2000) Triggering of cryoprotectant synthesis in the woolly bear caterpillar (Pyrrharctia isabella Lepidoptera : Arctiidae). J Exper Zool 286 (4): 367-371
  • Scoble, MJ. (1995) The Lepidoptera: Form, Function and Diversity. Second ed. Oxford University Press.
  • Simmons RB, Conner WE (1996) Ultrasonic signals in the defense and courtship of Euchaetes egle Drury and E. bolteri Stretch (Lepidoptera: Arctiidae). J Ins Behav 9 (6): 909-919
  • Simmons RB, Weller SE (2002) What kind of signals do mimetic tiger moths send? A phylogenetic test of wasp mimicry systems (Lepidoptera: Arctiidae: Euchromiini). Proc Roy Soc Lond B 269: 983–990
  • Wagner, DL, (2005) Caterpillars of Eastern North America. Princeton University Press.
  • Weller SJ, Jacobsen NL, Conner WE (1999) The evolution of chemical defenses and mating systems in tiger moths (Lepidoptera: Arctiidae). Biol J Linn Soc 68:557–578.

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