THE CATALPA SPHINX1 is a common hawk or sphinx moth, (Photo 1) but it is the caterpillar stage, (Photo 2), that is most often encountered and best known. The caterpillars, commonly called catalpa worms or "catawba" worms, feed on leaves of catalpa and often completely strip trees of foliage. Loss of foliage may be serious, especially for shade and ornamental trees and nursery stock. While the catalpa worm is well known as a tree pest, it may be as well or better known to some for its attractiveness to fish. The caterpillars have long been valued for fish bait, and references to their collection by fishermen date back at least to the 1870's when the species was first described (1).
Eggs, (Photo 3), are small, oval, about 0.66 mm long, 0.5 mm in diameter (1), and whitish, greenish, to cream-yellow in color. They are deposited in mound-like masses on the undersurface of leaves.
Larvae, or caterpillars, (Photo 2, Photo 4, Photo 5, Photo 6, and Photo 7), are white to pale yellow when first hatched, (Photo 4), and each has a conspicuous black spine or horn on the back at the rear, (Photo 5). As larvae grow, coloration changes; the head is black, the body whitish to pale yellow with black markings, (Photo 5). Full-grown caterpillars, (Photo 2, Photo 6, and Photo 7), are 70-75 mm long. Coloration is somewhat variable, and there appear to be two primary color phases, dark and pale. In the dark phase, (Photo 2 and Photo 6, bottom), there is a broad, solid black band down the back bordered by white lines. The sides are yellowish with some black spots and vertical lines. In the pale phase, the solid black band is lacking. Instead, there may be black spots along the midline of the back, (Photo 6), and/or narrow, broken black lines along the edges of the back, (Photo 7). Sides of the larva are generally greenish yellow.
The pupa, (Photo 8), is bare (no cocoon), reddish brown, and 30-35 mm long.
Infestations of the catalpa sphinx occur sporadically; they come and go and often seem to be highly localized. Certain trees appear to be preferred and are attacked regularly while others of the same catalpa species seem to escape attack; the reason for this is unknown. Caterpillars may be abundant for one, two, or three years, then scarce for several. Natural enemies such as parasites and predators, take a heavy toll of eggs and larvae, and are largely responsible for maintaining populations at low levels. One of the most common and important parasites is a small wasp that attacks the larva. The female wasp deposits eggs through the skin of the caterpillar. Wasp larvae feed and develop inside, then emerge to the outside and spin conspicuous white, silken cocooons on the caterpillar skin, (Photo 10). Parasitized catalpa worms do not survive to adulthood.
When caterpillars are numerous, infested trees may be completely defoliated. Defoliated catalpas produce new leaves readily and trees usually refoliate promptly. However, with multiple generations occurring, new foliage maybe consumed by subsequent broods. Most trees survive but some dieback may occur. Severe defoliation over several consecutive years can cause death of trees. Multiple defoliations of nursery stock, (Photo 11), may adversely affect survival of young trees when transplanted.
The catalpa tree, with its broad, dense crown and showy flowers, is prized by many as a shade or ornamental tree. Catalpa worms can essentially destroy this ornamental value. In this circumstance, the catalpa sphinx is a destructive, unwanted pest. However, there is another viewpoint. As indicated previously, catalpa worms are prized for fish bait. To many fishermen their presence is welcomed, even encouraged. Catalpa foliage is the only food of the catalpaworm, and it is likely that many catalpa trees are planted and maintained as much or more for production of fish bait as for any other purpose. Whether the catalpa sphinx is destructive or beneficial is a matter of point of view.
1Ceratomia catalpae. Order Lepidoptera; Family Sphingidae.
2One inch equals about 25 mm.
(2) Drooz, A. T. [ed.]. 1985. Insects of Eastern Forests. U.S. Forest Service Miscellaneous Publication 1426, 608 pp.
(3) Harrar, E. S. and J. G. Harrar. 1962. Guide to Southern Trees. Dover Publications, Inc., New York, 709 pp.
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All photos courtesy of Lacy L. Hyche