Is There a Way to Kill the Worms That Eat the Catalpa Tree?
- The worms feasting on your catalpa tree are actually caterpillars, or the larval stage of the Catalpa Sphinx moth. Catalpa Sphinx caterpillars begin as small, oval white, cream or green eggs laid in clusters of 100 to 1,000 underneath catalpa leaves. The eggs hatch in about a week, and the caterpillars that will consume your catalpa are born. They begin as white or yellow grubs with a black spine and horn extending from their ends, and grow into black and yellow caterpillars of about 3 inches in length. They feast for three weeks, and then transform into red-brown pupae before finally developing into adult moths. The Catalpa Sphinx moth is brown and gray and a little more than 1 inch long. The adult moth will not eat catalpa leaves. It's most active in mid-spring.
- The Catalpa Sphinx caterpillar feeds only on catalpa trees. The insect can strip an entire tree of its leaves within a day, depending on the number of worms in a colony. The leaf loss can cause problems in areas where the catalpa provides shade, or in nurseries, where gardeners cultivate the trees for sale. Newly hatched caterpillars chew only on leaf tissue between major veins, but as they grow, they move onto eating all live, green tissue. In warmer climates, as many as four generations of caterpillar may emerge in a single season. As your catalpa's leaves grow back, usually over six weeks, a fresh crop of caterpillars will be on hand to eat the new greenery. Such repeat defoliation can eventually kill younger catalpa trees.
- For maximum control of the Catalpa Sphinx caterpillar, catch the insects as eggs. Search the undersides of leaves for egg clusters, and remove and destroy affected foliage. To find emerging larvae, focus on the ends of branches. Cut off and destroy the infested branches. If your catalpa is larger, or if your worm infestation is substantial, pesticides with carbaryl, such as Sevin, can kill the worms. Insecticides with malathion or acephate will work as well. In autumn, turn the ground near your catalpa's trunk with a soil cultivator. Tilling will kill the pupae that over-winter in the ground and re-emerge in spring as egg-laying moths.
- Naturalists, including entomologists with Clemson University, advise against major measures to control the Catalpa Sphinx caterpillar, because infestations are sporadic. Nor do occasional infestations kill established catalpa trees. Catalpa Sphinx caterpillars also have natural predators that keep populations in check. The Apanteles congregatus wasp lays its eggs underneath the caterpillar's skin, where wasp larvae feed, and then emerge to build white cocoons outside the worm. If you spot these silky patches on your tree's caterpillars, the worms won't survive to adulthood. What's more, in some communities, the caterpillars are in high demand as fishing bait. In fact, the link between fishing and the caterpillars, also known as Catawba worms, is so strong that the catalpa tree is also called the fish bait tree or the fisherman's tree, according to scientists at the U.S. Department of Agriculture.