Moths of North Carolina
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149 NC Records

Acharia stimulea (Clemens, 1860) - Saddleback Caterpillar Moth

Taxonomy
Superfamily: Zygaenoidea Family: LimacodidaeP3 Number: 660055.00 MONA Number: 4700.00
Comments: This is one of two representatives of this genus that occur in North America and the only one that is found in North Carolina. This species was placed in the genus Sibine in older references.
Identification
Field Guide Descriptions: Covell (1984; as Sibine stimulea); Beadle and Leckie (2012)Online Photographs: MPG, BugGuide, iNaturalist, Google, BAMONA, GBIF, BOLDTechnical Description, Adults: Forbes (1923)Technical Description, Immature Stages: Wagner (2005)                                                                                 
Adult Markings: Acharia stimulea is the largest of our slug moths, with the length from the tip of head to the apex of the forewing at rest averaging 18.5 mm (n = 5) for North Carolina specimens. The body is stout and dark brown, with heavy, brown, furry legs and broad, dark reddish-brown to dark brown forewings. The only conspicuous marks on the forewing are white dots, with one (occasionally two) centered near the base of the forewing and two (rarely one or three) in the subcostal region at around three-fourths the distance from the wing base to the apex. There are also broad longitudinal swaths of silvery-blue scales that are largely concentrated through the middle of the wing, along the costa, and along the inner margin. These impart a shiny appearance when stuck by light at certain angles. When combined with brown or reddish-brown areas that lack the silvery-blue scales, it gives the forewing a distinctive appearance.
Wingspan: 2.6 - 4.3 cm, with females larger than the males (Covell, 1984).
Adult Structural Features: The male antenna is pectinate at the base and simple in the outer half, while the hind tibia has only a single pair of spurs (Forbes, 1923).
Adult ID Requirements: Identifiable from good quality photos of unworn specimens.
Immatures and Development: The larvae are highly polyphagous and feed on a very wide variety of plants. The females lay masses of 30-50 eggs on the upper sides of the leaves of the host plant, and the hatchlings typically emerge around 10 days later (Dyar and Morton, 1896). The early instars commonly feed communally on both sides of the leaves and skeletonize them by scraping off patches of tissue with their mandibles. Around the third or fourth instar, they transition to group edge-feeding and consume the entire leaf tissue except for the tougher veins. The oldest instars consume the entire leaf, including the veins (Bibbs and Frank, 2012). Group feeding may help to ward off predators and increase growth by rapidly consuming the leaves before the host plants can synthesize defensive allelochemicals (Fiorentino, 2014). The larval stage last 4-5 months and has eight instars. The final-instar larvae spin tough, fibrous cocoons and incorporate stinging spines and calcium oxalate into them (Bibbs and Frank, 2012; Fiorentino, 2014). Overwintering occurs in the pupal stage on the ground.

The larva is among the most distinctive of all caterpillars. It has a lime green saddle with a brown center. Both the outer margin of the saddle and the brown center are edged with white. There are several pairs of lobes on the thorax and a matching set of large lobes on the posterior end that bear long, stinging spines with venom that pack a formidable sting when contacted by skin. The sting is described by Wagner (2005) as being among the most potent of any North American slug caterpillar, a claim that can be attested to by many gardeners. The sting is typically accompanied by local redness and swelling, and even blistering if the spines are not quickly removed (Diaz, 2005).
Larvae ID Requirements: Unmistakable and widely known.
Distribution in North Carolina
Distribution: Acharia stimulea occurs throughout much of the eastern US and adjoining areas on southern Ontario, as well as in Central America and northwestern South America. In the US the range extends from Massachusetts and Connecticut southward to southern Florida, and westward to eastern Texas, Arkansas, eastern Oklahoma, Missouri, northeastern Kansas, southeastern Nebraska, Illinois, and southeastern Iowa. This species occurs statewide in North Carolina, from the barrier islands to higher elevations in the Blue Ridge, but is relatively uncommon in the Coastal Plain where hardwoods are less prevalent.
County Map: Clicking on a county returns the records for the species in that county.
Flight Dates:
 High Mountains (HM) ≥ 4,000 ft.
 Low Mountains (LM) < 4,000 ft.
 Piedmont (Pd)
 Coastal Plain (CP)

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