Most people wouldn't expect to see a moth on a list of bad but beautiful organisms, yet at least one may have earned the dubious honor. Unlike the boring-brown moths that flutter around porch lights, the oleander moth (Syntomeida epilais Walker) is lovely to behold, with its glittering blue-green body and shimmery wings. The jewel-like body is dappled with white spots and the insect's reddish-orange abdomen adds to its colorful appearance. Oleander moths are active in the daytime, flying around the garden on an endless reconnoiter in search of tasty foliage -- and oleanders (Nerium oleander), suitable in U.S. Department of Agriculture plant hardiness zones 8 through 10, are its favorite food.
Description and Life Cycle
Often called polka-dot wasp moth because of its body shape and the white spots on its legs, antennae and body, oleander moths can generally be found wherever oleanders grow, except California, and lay clusters of cream to pale yellow eggs on the undersides of oleander leaves. The larvae damage but do not kill oleanders. The moth's larvae are orange caterpillars with clumps of black hairs growing from the bumps on their bodies. When the caterpillars are ready to transform into moths, they gather in clusters inside tan cocoons tucked here and there on the oleander, nooks in tree trunks or the crevices where walls and eaves of buildings meet.
While in the young, gregarious stage, oleander caterpillars feed on the undersides of the plants' leaves, causing the foliage and tender new shoots to brown. Leaves may be skeletonized. Older caterpillars can defoliate the entire plant, weakening the oleander enough for other insects to join the attack.
The usually unpopular red imported fire ant can be an asset during an oleander caterpillar infestation, because the ants eat pupa inside their cocoons. Predatory stink bugs, parasitic wasps and tachnid flies may also feed on oleander moth larvae. Naturally occurring pathogens can infect the larvae, turning them dark and flabby. According to the University of Florida's Featured Creatures website, these sickly caterpillars should be left on the plant to help spread the disease. Because all parts of the oleander plant are poisonous, most birds and common predatory insects steer clear of oleander caterpillars.
If you can stand the thought of caterpillars sharing freezer space with your food, large caterpillars can be plucked off the plants by hand, placed in a plastic bag and frozen to death. Masses of caterpillars or cocoons can also be removed by pruning infested foliage. Bag the cuttings and freeze them. Larger caterpillars handpicked from the plant may be dropped into a container of soapy water rather than frozen. Monitoring the plants and removing egg clusters can reduce potential infestations. Use caution when handling oleander plants, because the sap can irritate your skin and all parts of the plant are highly toxic.
Although several pesticides are available to kill caterpillars, most also harm other, beneficial insects. As a last resort, pesticides sprayed while the caterpillars are in their young social stage can control extremely heavy, damaging infestations. Bacillus thuringiensis (Bt) targets caterpillars and doesn't harm most other insects. The product kills all types of caterpillars, however, including future butterflies. To control oleander caterpillars with concentrated Bt pesticide, mix 4 teaspoons of pesticide into 1 gallon of water. Fill a sprayer reservoir and thoroughly spray the oleander's foliage, including the undersides of the leaves. Do not spray to the point that the pesticide runs off the plant.
- University of Florida IFAS Extension: Oleander Moth
- University of Florida Entomology Department: Featured Creatures –- Oleander Caterpillar: Syntomeida Epilais Walker
- University of Georgia Cooperative Extension: Insect Fact Sheet -- Oleander Caterpillar (Syntomeida Epilais Jucundissima)
- University of Florida IFAS Extension: Oleander Caterpillar -– Syntomeida Epilais
- Bonide: Bacillus Thuringiensis (BT) Thuricide Concentrate
- Missouri Botanical Garden: Nerium Oleander
- Photo Credit Thinkstock/Comstock/Getty Images