Extension Service: Spanworms won't kill bushes, but they're doing damage this year

At first, the caller thought I had mentioned a new computer virus, but no — this is the snowbush spanworm, not "spam worm." Depending on your point of view, your snowbush shrubs (Breynia nivosa) may be getting a free pruning! The snowbush caterpillar is more abundant this year than in previous years and is stripping the foliage from these attractive shrubs.

Caterpillar populations may increase if parasite or predator activity has declined due to too much rain or the normal predator-prey fluctuations. Usually snowbush hedges will re-sprout in a short time. To make matters worse, however, some properties may have so many caterpillars that after the foliage is eaten, they start chewing on the twigs. The yellow and black larva or caterpillar is the immature stage of a pretty moth called the white-tipped black. This feeding machine's metered, looping crawling style gives it away as a member of the "inchworm" family of moths, also known as "spanworms."

Inchworms have fewer abdominal legs than many other caterpillars, hence they stretch out the length of their bodies and pull their rear section up quickly, which forms a loop as they move; much like a slinky toy going down steps. At about an inch long, the larva is full-grown and is ready to change into a pupa. It enters the soil, er, sand, goes through the changes there, and emerges as a moth in about seven days, according to local lepidopterist Mike Malloy. This is a day-flying moth, which is unusual, because the modus operandi for most moths is as covert, nighttime navigators. The moths have a striking velvety appearance; navy-blue black, with white tips on each of the four wings and an orange thorax.

On June 21, Mike and I examined some snowbush hedges in the West Crowne Pointe area. Some of these hedges were 50 percent defoliated. The hedges had mature caterpillars as well as newly hatched larvae, less than 1/8th inch in length. This tells us that a new generation will be appearing with more damage on the way. It's not certain how many generations there are, but we will be keeping close track this year.

The snowbush spanworm also attacks Otaheite gooseberry (Phyllanthus acidus), and supposedly white sapote (Casimiroa edulis), and snow-on-the-mountain (Euphorbia marginata). If you don't enjoy the colorful, slinky inchworms and pretty moths, a spray solution with a spinosad-containing insecticide product would be a narrow spectrum insecticide choice similar to B.t.

Doug Caldwell is landscape entomologist and commercial landscape horticulturist works for the Cooperative Extension Service of Collier County. . E-mail dlcaldwell@ifas.ufl.edu Call 353-4244 x203. Extension programs are open to all persons without regard to race, color, creed, sex, handicap or national origin. For updates on the Southwest Florida Horticulture Learning Center and more landscape pest management details, visit http://collier.ifas.ufl.edu.

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