Devil’s potato, Polka-dots & Ultrasonic Communication

Devil’s potato (Echites umbellatus) is a relatively rare woody vine of beach strand and, further south, pine rocklands. It grows only on the southeast coast of Florida and only as far north as Brevard County. Seeing it in flower at Treasure Shores Park on 6/3/2017 was unexpected. One lone plant was clambering over saw palmetto not far from the beach dune.

Also commonly called rubbervine, this vine has thick, rubbery paired (opposite) 2” leaves that are salt and wind-tolerant. Its genus name, Echites, comes from the Greek word for viper, referring to its snakelike twining stems.

White trumpet-shaped flowers with 5 fringed petals appear all year, peaking in summer. The species name, umbellatus, refers to the umbellate arrangement of its flowers. Umbellate flowers spread out from a common point.

The common name, devil’s potato, refers to its poisonous, tuberous root. In fact, all parts of this plant, a member of the Apocynaceae (dogbane) family, are poisonous including its milky sap. Oleander (Nerium oleander) is another poisonous member of this plant family.

The polka-dot wasp moth (Syntomeida epilais) once used devil’s potato as its preferred larval host plant — until the introduction in the 17th century of oleander, a Mediterranean ornamental plant. The polka-dot wasp moth is so enamored with oleander that it is now often called the Oleander Moth. “Oleander caterpillars can defoliate a plant in a week or two”, according to EDIS, the Electronic Data Service of the University of Florida/Institute of Food and Agricultural Sciences Extension.

Its caterpillars are orange with clumps of blacks hairs arising from black bumps (tubercles) on its body. They do not sting and can be handled without harm, though at a glance they appear to have urticating (stinging) hairs. They sequester poisons from the plants on which they feed, so birds and small mammals do not feed upon them.

The adult moths are striking with an iridescent blue-green body and wings decorated with small white polka-dots and contrasting red/orange spot on the tip of its abdomen. At a glance, this moth appears to be a wasp. This mimicry and its bright coloration which “advertises” its poisonous nature allow this slow-flying moth to be active during the daytime. Most moths are nocturnal.

Most butterflies and moths communicate via pheromones but not the polka-dot wasp moth, the first moth to be shown to communicate with ultrasonic signals. Think bats!

During the early 1990’s, Mark V. Sanderford, a “night-owl”, spent his summers at the Florida Medical Entomology Laboratory (FMEL) documenting its unique mating behavior. He showed that female moths emitted an acoustic signal that could not be heard by humans but that could attract male moths from a long distance. With special acoustic equipment, he recorded the courtship duet of acoustic calls that took place prior to mating about 2 or 3 hours prior to dawn and played back the acoustically-enhanced clicks of courtship for human ears.

The Polka-dot Wasp Moth is not the only to use devil’s potato as a larval food, but it is quite unique, Other moths that use devil’s potato include the Faithful beauty moth (Composia fidelissima), a red, white, and blue tropical moth sometimes called the Uncle Sam moth, shown below, and the tetrio or giant gray spinx moth (Pseudosphinx tetrio).

The caterpillar and moths photographs are from the University of Florida Department of Entomology and Nematology.

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