Catalpa Worm/ Catalpa Sphinx Moth

Classification

Common names: catalpa worm (caterpillar), catawba worm (caterpillar, primarily in the southern US), catalpa sphinx (adult moth)

Scientific name: Ceratomia catalpa (Boisduval, 1875)

Family: Sphingidae (sphinx moths)

Order: Lepidoptera (butterflies and moths)

Summary

Catalpa worms are occasional pests that may defoliate catalpa trees during outbreak years. However, they are a native species that are attacked by a host of natural enemies, so control is often not warranted.

Distribution

Catalpa sphinx are native to the eastern United States and can be found wherever catalpa trees occur from New Hampshire and Nebraska south to the Florida and Texas (Figure 1). This species has historically been found in Maine and northern New England but may now be absent from that region.

Description and Identification

Like other sphinx moth caterpillars, catalpa worms possess a stiff "horn" near the end of the abdomen, which is relatively long, straight, and black compared to other species. Young caterpillars are mostly white with black spots. Older caterpillars are variable in color and can range from mostly yellow to almost entirely black, although most are black dorsally with a broad, yellow stripe on the side (Figures. 2a-c).  Regardless of coloration, catalpa worms are the only species of sphinx moth that that feed on catalpa, so positively identifying the host plant can aid in identifying the caterpillars. Additionally, catalpa worms are the only sphinx moth caterpillars that feed gregariously through the third and sometimes fourth instar.

Adult moths are large, brown moths with thick, cigar-shaped bodies (Figure 3). The forewings possess a grey spot that is rimmed in black. Unlike other commonly encountered, similarly colored sphinx moths (e.g., tomato hornworm), catalpa sphinxes lack yellow spots on the abdomen.

Host Plants

Catalpa worms feed exclusively on trees in the genus Catalpa, including native northern and southern catalpa (C. speciosa and C. bignonioides, respectively) as well as non-native species like Chinese catalpa (C. ovata) that are occasionally planted as ornamentals.

Life History

Pupae overwinter in soil around the base of the host tree. Adult moths begin to emerge in April and can be found through October. Masses of 100–1,000 eggs are laid on the underside of catalpa leaves. Caterpillars are present from May through November. Only one generation occurs in northern areas, including Pennsylvania, while up to five generations can occur in southern areas (e.g., Louisiana).

Catalpa sphinx moths are a boom-and-bust species. The caterpillars may be difficult to find or even completely absent from an area for one to a few years before outbreaking for one to a few years.

Because they are a native species, catalpa worms are attacked by a number of natural enemies, including various wasp and fly parasitoids. The most common parasitoid that attacks catalpa worms are Cotesia congregate wasps. Cotesia pupae are the most obvious stage as heavily infested caterpillars can be covered in dozens of white cocoons (Figure 4). Cotesia congretata also parasitizes other sphinx moth caterpillars, including tomato and tobacco hornworms; interestingly, there is apparently little gene flow between catalpa worm- and tomato hornworm-infesting populations such that they may be in the middle of becoming distinct, host-specific species.

Control

During non-outbreak years, natural enemies often exert enough control on catalpa worms that additional control measures are unnecessary or even detrimental as catalpa sphinx populations, especially in the south where multiple generations occur, may recover faster than natural enemies and outbreak sooner than they would have.

Healthy catalpa trees can withstand complete defoliation by catalpa worms and will often push out a second set of leaves if defoliation happens early in the season. So one tactic is to ensure catalpa trees are healthy enough to withstand defoliation via proper water and fertilizer regimes and accept sporadic catalpa worm outbreaks as a consequence of growing catalpa trees. During large outbreaks, smaller individual branches may be killed, but this is unlikely to affect the long-term health of the tree.

Repeated outbreaks of catalpa worms over multiple seasons or multiple outbreaks in one season where multiple generations occur may damage and kill catalpa trees, especially trees that are already weakened by stress or disease. Some trees are defoliated more frequently and may be more attractive to catalpa sphinxes than others. The reasons for this are unclear but may be tied to the genetics of individual trees. If an individual tree is continuously defoliated by catalpa worms and appears to be in decline, it may be best to remove and replace it with a catalpa with different genetics or with a different tree species altogether.

If control is desired, there are a number of tactics that can be employed. First, egg masses, which are often obvious on the undersides of leaves, can be removed and destroyed. When catalpa trees are small, the caterpillars can be trimmed out (if they're young and gregarious) or handpicked and drown in a bucket of soapy water. Caterpillars that are parasitized should be left on the tree in order to allow the parasitoids to emerge. In the fall or early spring, after the caterpillars burrow into the soil to pupate and before the adult moths emerge, the soil around the tree can be tilled in an effort to destroy the pupae. When caterpillars first emerge and are small, products that contain Bt can be applied to the tree to kill them. Broad-spectrum insecticides should be avoided because of their detrimental impacts to natural enemies, which may make subsequent outbreaks worse.

Uses

Catalpa worms are sometimes used as fishing bait, especially in the southern US. They are apparently an excellent bait for largemouth bass and catfish and some dedicated fishermen have been known to drive many miles or plant small groves of catalpa trees in order to secure a ready supply of catalpa worms. A patent for preserving live catalpa worms for bait was filed in 2003.

Warning

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

References

Bowers, M.D. 2003. Hostplant suitability and defensive chemistry of the catalpa sphinx, Ceratomia catalpa. Journal of Chemical Ecology, 29(10): 2359–2367.

Butterflies and Moths of North America, catalpa sphinx. 2017. Lotts, K. and T. Naberhaus (coordinators).

Catalpa ovata. 2019. Missouri Botanical Garden Plant Finder.

Coder, K.M. 2018. Important tree species – Southern catalpa, Catalpa bignonioides: The fishing bait tree. Arboretum 18-17. 15 pp.

Comeaux, M. 1989. Hook-and-line fishing in the Mississippi River System. Material Culture 21(1): 23–45.

Gilman, E.F., and D.G. Watson. 1993. Catalpa spp. Fact sheet ST-130. Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. 3 pp.

Howard, L.O., and F. H. Chittenden. 1918. The catalpa sphinx. Farmers Bulletin, Bulletin 705. United States Department of Agriculture, Washington, D.C.

Kester, K.M., G.M. Eldeib, and B. L. Brown. 2015. Genetic differentiation of two host-foodplant complex sources of Cotesia congretata (Hymenoptera: Braconidae). Annals of the Entomological Society of America, 108(6): 1014–1025.

Sipe, W.A. Method of preserving live Ceratomia catalpae larvae for use as fishing bait. US Patent 7,429,398 B1 filed 26 August 2003, granted 30 September 2008.