Two species of catalpa trees exist in North America, northern catalpa (Catalpa speciosa) and southern catalpa (Catalpa bignonioides). The word “catalpa” derives from the Native American word for trees of this type, “catawba.” These trees live throughout the United States, inhabiting all areas but the upper Midwest, and reach a common mature height and spread of 50 feet. Catalpa trees exhibit sensitivity to pests and diseases and suffer greatly from infestations of a particular worm.
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The catalpa sphinx moth (Ceratomia catalpae) lays eggs on catalpa trees in early April or May. Its habit of only laying eggs on catalpa trees earned the larvae of the month their common nickname, catawba worms. A single female moth possesses the capability to lay as many as 1,000 eggs at once. Larvae emerge from the eggs after 10 to 14 days. These larvae display a black spine and green skin and feed heavily on catalpa trees. They reach a mature length of only three inches. Catalpa sphinx larvae belong to the hornworm group of insects.
Catawba Worm Cycle
Catalpa sphinx eggs induce a naturally occurring cycle. The worms eat leaves of trees and severe infestations can completely defoliate a large tree in a single growing season. Even minor infestations cause extensive defoliation. By chewing on the leaves of catalpa trees, catalpa sphinx caterpillars induce the increased secretion of nectar. This increased secretion attracts the presence of ants, ladybugs and other natural predators of catalpa sphinx larvae. These insects eradicate the presence of remaining worms and harvest nectar from the tree, which encourages pollination.
Managing Catalpa Sphinx
Catalpa sphinx only need be managed when extensive infestation occurs over the course of a number of growing seasons. A single infestation causes partial or complete defoliation, though catalpa trees readily grow new foliage upon first defoliation. Furthermore, many catalpa moth infestations occur in highly localized regions of a tree and may not spread throughout the entire specimen. Despite this, repeated defoliation over the course of multiple seasons can cause die back or in extreme cases the death of the tree. Catalpa sphinx can be managed in a number of ways, including simply removing caterpillars from the tree by hand or introducing natural predators like ladybugs. The use of insecticidal soaps with Bacillus thuringiensis proves effective. Chemical control should only be used in cases of extreme infestation.
Intentionally Harvesting Worms
Some growers cultivate catalpa trees for the express purpose of attracting catalpa sphinx larvae. Once catalpa eggs hatch these growers collect them and either sell them or use them as fishing bait. Fishermen hold the catawba worm in high esteem for its ability to attract fish. In warm climates, catalpa sphinx can produce as many as three generations between April and November. Growers harvesting catawba worms for commercial purposes walk a fine line between maximizing larvae productivity and allowing larvae to destroy a tree, thereby ruining its ability to attract future generations.