Large Green Caterpillars in South Florida That Eat Hibiscus Plants

Adult Io Moths

• Although an adult Io moth's 2- to 3 1/2-inch wingspan is impressive, it's only average for a moth of its family. The Io moth's brilliant color and markings more than compensate for what it lacks in size. The larger female's rust-red and mauve forewings hide its rust- and black-ringed tangerine rear wings. Her rear wings -- and those of the yellow-orange, feathery-antennaed males -- boast showy, white-centered bluish-black eyespots. The one exception to these color combinations is the Automeris Io lilith subspecies common in southern Florida. Its male adults have reddish-brown forewings.

Caterpillars

• Io moth caterpillars hatch from clumps of creamy-white eggs the females deposit on hibiscus stems and leaves. Orange to orange-brown at birth, they spend their early lives feeding in groups and traveling over the hibiscus in single file. After five stages, or instars, they've reached 2 1/2 inches, with flashy red-and-white pinstripes adorning their pale green sides. Clusters of bristles emerging like porcupine quills from raised areas on each of their 13 segments protect the caterpillars from birth. Gray at first and yellow or green with branching black spines later, the bristles deliver a hefty dose of toxins to any creature unfortunate enough to break them. For people, this typically results in several hours of painfully stinging, inflamed skin. Wear gloves if you're working around a plant with these caterpillars.

Life Cycle

• Io moths produce two to four generations of caterpillars each year on hibiscus in the warmer areas of the plants' growing range in U.S. Department of Agriculture plant hardiness zones 4 through 11. In South Florida, the caterpillars may be present all year. After several weeks of feeding, the caterpillars drop to the ground and spin papery brown cocoons. The newly emerged adults mate, lay eggs and die without eating.

Management

• Because one encounter is it all it takes for birds or other natural predators to steer clear of Io caterpillars, you'll have to assume responsibility for protecting your hibiscus. The best way to manage the pests without endangering yourself is to monitor your hibiscus for eggs. As soon as the caterpillars hatch, spray them with a solution of 1 or 2 teaspoons -- or the manufacturer's specified amount -- of wettable Bacillus thuringiensis powder per 1 gallon of soft water. Young Io caterpillars ingesting the Bt organisms develop digestive impairment, stop feeding and eventually starve. Applying freshly mixed solution when no sun is striking the plants brings the best results.