These caterpillars are eating the leaves of live oaks, post oaks, water oaks, and even crepe myrtles, but rest assured, they will not kill your trees. This insect undergoes only one life cycle each year, so in a couple of weeks they will be forming cocoons, and in June they will begin to emerge as moths. Once they enclose themselves in cocoons, the leaf-feeding will stop and trees will start to put on new leaves. Healthy trees can recover from a complete defoliation 3-7 times in one year. The tree will use energy reserves stored in the roots to make new leaves.
So what can you do about these pests? I only recommend spraying high-value trees or trees that hang over a patio or walkway, where the webs will be a serious nuisance to people. The caterpillars are a natural part of the local ecosystem, thus, birds and many other predators probably look forward to each spring and the worm-buffet that comes with it. While the caterpillars are small (less than 1 inch) I recommend liquid insecticides containing Bt (Bacillus thuringiensis), a naturally occurring bacteria that targets only caterpillars and poses no threat to beneficial insects, pets, or humans. This product is commonly used in organic gardening. Sprays such as malathion or carbaryl (Sevin) are broad-spectrum insecticides that can potentially kill beneficial insects, but will also work to control the caterpillars.
Insect populations cycle up and down naturally. Next year we may have very few caterpillars, or we may have more than this year. Keep an eye out during the first of April next year to determine if and when you may want to spray.
By Stephen Janak, County Extension Agent – Ag/Natural Resources