What is the polka-dot wasp moth?

By Chelsie Vandaveer

October 8, 2003

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Rose bays or oleanders (Nerium oleander Linnaeus) are members of the Apocynaceae, the dogbane family. These decorative shrubs were introduced to the New World by Spanish settlers sometime during in the seventeenth century. The foliage is eaten by the oleander caterpillar (Syntomeida epilais Walker), a member of the Ctenuchinae, or wasp moths.

The caterpillars are orange with long black setae or hairs. The caterpillars look dangerous, but the setae are not nettling and cannot sting. The caterpillars are gregarious; the siblings feed in groups. If not controlled, the caterpillars will strip the shrub. The plants recover, but are weakened and susceptible to diseases and other pests. Although, usually found on oleander, these caterpillars may be found devouring desert rose (Adenium spp.) or other dogbanes.

Oleander Moth, Also Called Polka-Dot or Uncle Sam

Although, usually found on oleander, these caterpillars may be found devouring
desert rose (Adenium spp.) or other dogbanes.
Oleander Moth, Also Called Polka-Dot or Uncle Sam Photographic Print
James H. Robinson
Buy Photographic Print at AllPosters.com

According to Heather McAuslane with the University of Florida, the adult stage is called the oleander or polka-dot wasp moth. The moth's wings are shaped like a wasp's wings; they are bluish-black with a few white polka-dots. The moth's abdomen is blue and bright red. It looks like a very dangerous wasp or hornet, but it is harmless.

Female polka-dot wasp moths do not release pheromones to attract males for mating. In the evening, a female perches on a branch and emits ultrasonic (above human hearing) signals that travel great distances. The males follow the 'song' to her location. When a male is within several meters of the female, he emits an answering ultrasonic signal. The two call back and forth until mating before dawn.

Oleander moths were not imported with oleanders to the New World. The moths are native to the Caribbean. It is thought that the devil's potato (Echites umbellata Jacquin) was once the main host plant for the caterpillar. Importation of oleanders benefited this pest; they switched host plants and have increased their range. Except for California, the polka-dot wasp moth is now found wherever there are oleanders in the Americas. ("Oleander Caterpillar", Heather McAuslane, IFAS, University of Florida, 1997)

Institut National de la Recherche Agronomique has a great close-up of the polka-dot wasp moth. To view the photograph, click on the link:

http://www.inra.fr/papillon/arctiid/textfr/s_epilai.htm

"Whats this caterpillar" has a great photograph of oleander caterpillars on their host plant. To view the photograph, click on the link:

http://www.whatsthiscaterpillar.co.uk/Caterpillars%20submitted/slides/gulffritillary.html

This is a fun and informative website. To go to the home page, click on the link:

http://www.whatsthiscaterpillar.co.uk

The Atlas of Florida Vascular Plants, Institute for Systematic Botany, University of South Florida has several photographs of the beautiful white-flowering devil's potato, Echites umbellata, the original host plant for the oleander caterpillar. To view the photographs, click on the link:

http://www.plantatlas.usf.edu/main.asp?plantID=3816

Click on the Images tab and on the thumbnails to enlarge the images.

The oleander caterpillar superficially resembles the gulf fritillary caterpillar which gets many of these butterfly caterpillars killed by well-meaning, but uninformed gardeners. Oleander caterpillars are never found on passionflowers (Passiflora spp.) and gulf fritillary caterpillars are not found on oleanders, except maybe crawling there to pupate. University of California, Irvine, CA has a beautiful photo layout of all stages of the gulf fritillary's life cycle. To view this layout, click on the link:

http://www.dbc.uci.edu/~pjbryant/biodiv/lepidopt/nymph/gulf.htm

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