Observations on larval development of the saddleback caterpillar (Acharia stimulea: Limacodidae)

A classic form of aposematism is found in the larvae of species Acharia stimulea, a bizarre member of family Limacodidae that occurs quite commonly in eastern North America. Mid- to late instars of this peculiar caterpillar are characterized by a conspicuous lime green dorsal "saddle" (hence the species' common name, the 'saddleback'), which is centered by a distinct black oval with a white peripherical ring. Two pairs of noticeable scoli exist at either end of the body, the uppermost scoli being considerably longer and more conspicuous. A long chain of warts outline the caterpillar, each of which is armed in dozens of poison-filled spines. These spines are undoubtedly an effective means of defense for the larva, causing severe rash and irritation in even humans who are unfortunate enough to come in contact with these poison-filled barbs. To the author, the sting is much like that of hand sanitizer on a wound but is longer lasting. Larvae are frequently gregarious, feeding in a noticeably polyphagous manner; while it appears this degree of feeding is greater than all other eastern North American slug caterpillars, this cannot be said for certain, as A. stimulea feeding records are probably observed much more frequently than those of other limacodids due to their abundance and aposematism. Adults of A. stimulea are likely the largest among eastern North American limacodids, the females capable of exceeding 2.0 cm in FW length from base to apex. Although female saddlebacks are the largest , the males may be equaled or exceeded in size by a few species (e.g., Prolimacodes or Parasa). The FW is chocolate brown in both sexes accompanied with several white spots in the apex and roughly the center of the wing (roughly the inner margin). The adults are attracted to lights, though they have been recorded as uncommon (Covell, 1984: 411) and are at least not nearly as common at lights as many other species (e.g., Apoda, Euclea). In comparison to most other eastern North American limacodids, females seem to be more common than usual. Inaturalist (https://www.inaturalist.org/taxa/122228-Acharia-stimulea) (accessed 06 October, 2021) records 124 males to 118 females. To put this in comparison, Inaturalist (https://www.inaturalist.org/taxa/136548-Euclea-delphinii) (accessed 06 October 2021), recording Euclea delfinii, another well-known limacodid in eastern North America, lists annotations for 633 males to 102 females. Most other species (e.g., Apoda biguttata and Isochaetes beutenmuelleri) follow the example of E. delphinii, indicating that males are considerably more abundant than females in most Limacodidae in eastern North America. Hence A. stimulea adults seem to stick out in regards to sex abundance from the rest of the group.

On September 06, 2021, a mid-instar A. stimulea was collected in Harrison County, WV, on Quercus alba (white oak) (see observation attached for more geographical information) https://www.inaturalist.org/observations/94348839. The larva was subsequently reared on foliage from the same tree. Subsequently, various host plants were offered, which are as follows: Quercus alba, Q. velutina, Acer saccharum, Fraxinus americana, Celtis occidentalis, Ulmus rubra, Malus pumila, Yucca filamentosa, Morus alba, Juglans nigra, Cornus florida, Liriodendron tulipifera, Catalpa speciosa, and Prunus serotina. Of these, Q. rubra, Q. velutina, A. saccharum, F. americana, C. occidentalis, and M. alba were readily accepted by the larva. U. rubra, Y. filamentosa, J. nigra, C. speciosa, L. tulipifera and P. serotina were accepted, but reluctantly by the larva. Interestingly, the caterpillar would not eat M. pumila or C. florida. Age or condition of the foliage did not seem to be of significant importance, the larva going both to soft or hard foliage.

As any observer notes, the only notable area on the larva without spines is the dorsal saddle. The author decided to experiment with this 'Achilles' heel', and the results were quite interesting: a pencil tip was placed on the dorsal saddle, and the larva instantly bucked its spine-tipped scoli at the pencil, attempting to spine its supposed predator (see observation image 4). Hence this larva was extremely aggressive, well aware of its effective venom-filled weaponry.

Literature cited: Covell, Charles V. Eastern Moths. (New York: Houghton Mifflin Company, 1984), 411.

Publicado el sábado, 02 de octubre de 2021 a las 02:09 AM por tcooley tcooley

Observaciones

Fotos / Sonidos

Autor

tcooley

Fecha

Septiembre 6, 2021 a las 07:36 PM EDT

Descripción

Found on Q. alba. Cocoon (see images) constructed on October 04, 2021.

Comentarios

@marcepstein Check updated version

Anotado por tcooley hace casi 2 años

@tcooley Thanks for the updated version. It adds a lot of important info to the previous!

Anotado por marcepstein hace casi 2 años

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