What to Know About Catalpa Trees and Their Worms

Catalpa trees, with two species native to the United States, are known for their beautiful and plentiful blooms and for being the sole source of food for catalpa worms—caterpillars that strip the tree of its foliage and eventually become the catalpa sphinx moth.

Though catalpa worms can completely defoliate a catalpa tree during a single summer, healthy trees typically recover the following year, and natural predators keep the worms from doing too much damage in the long term.

Because the worms are native, they have ample natural predators, including various wasp and fly parasitoids. Worms from the catalpa tree have long been valued as fish bait, and some fishermen plant the trees solely for this purpose. When fully grown, they’re around two-and-a-half to three inches long and somewhat variable in color, though primarily either dark or pale with a black stripe or dots down the middle of the back.

Catalpa Worms and Braconid Wasps

The endoparasitoid wasp, Cotesia congregata from the Braconidae family, is the primary predator of catalpa worms. These wasps lay eggs along the back of the caterpillar; after the wasps hatch, they feed on the worm itself, eventually killing it. The wasps also inject venom into the caterpillars to control the worm's development. Endoparasitoid wasps benefit the catalpa trees and the ecosystem because they help stop the worms from killing the tree.

The Catalpa Tree

The two species of catalpa tree native to the United States—northern and southern catalpa—have a current distribution from New Hampshire and Nebraska in the northern United States and from Florida to Texas across the South. Historically, the southern catalpa is native from northern Florida to Georgia, and west through southern Alabama and Mississippi. The northern catalpa’s natural range is along the confluence of the Mississippi and Ohio rivers from Southern Illinois and Indiana to northeastern Arkansas.

Like the names of many places, plants, and rivers across the United States, the word catalpa originates from a Native American term, the Creek word catalpa, meaning “winged head,” and the Muskogee tribe used it to refer to trees. The tree’s name is also spelled catawba (which is how catalpa is pronounced). Some fishermen refer to the catalpa as the “fish bait tree,” and it has been referred to as “cigar tree” or “bean tree,” because both the northern and southern species feature long, slender seed pods that look like a cigar or an unshelled long bean. The northern catalpa has pods that are slightly slimmer in diameter and up to two feet long, while the southern catalpa usually has pods less than 12 inches long. Both varieties produce large, white, erect flowers.

Catalpas are dual pollinators—bees pollinate the flowers in the daytime, guided by the yellow and purple markings (nectar guides). Then, at night, increases in nectar and fragrance attract moths (including the catalpa sphinx) to continue the pollination process. Catalpas also tolerate many soil types, including compacted soil, and can grow near pavement. Despite their native range being largely confined to the southeastern United States, the trees flourish as far north as New Hampshire—meaning they’re fairly climate tolerant.

Historically, catalpa trees have served a variety of uses and have been extensively propagated for more than 200 years. European settlers used the wood for fence posts, and railroad companies used it to make track ties and fuel wood. Carpenters commonly turn to catalpa wood for interior trim in houses, and craftsmen love it for furniture. Catalpa wood has also been used to construct telephone and power line poles. The wood is lightweight, and the heartwood is resistant to deterioration when placed in the ground for several years.

The southern catalpa tree also has medicinal uses—a tea made from the bark has been popular as an antiseptic, snake bite antidote, laxative, sedative, and tincture to remove parasitic worms. This tea has also been used as a substitute for quinine in treating malaria. A tea made from the seeds was a go-to treatment for asthma and bronchitis as well as a rinse on wounds. In addition to having a sedative effect, the plant is reported to have mild narcotic action and it's used for the treatment of whooping cough, asthma, and spasmodic coughs in children. Contemporary pharmaceutical research has shown catalpa trees have diuretic properties. Take care when using the catalpa tree for healing, however, as the tree's roots are poisonous and shouldn't be handled or composted. Despite its many positive attributes and ability to attract pollinators, catalpa trees don't seem to be planted particularly often around the United States. Gardeners have attributed this to their distinctive odor and the mess left behind as their seed pods drop to the ground in the spring. These pods can disperse widely, leading quickly to new catalpa sprouts.

Catfish Candy

Written references to catalpa worms as prized fishing bait date back to the late 1800s, and fishermen have likely planted the trees to have a steady source of bait since before then.

For sustenance fishing, a few catalpa trees could provide enough worms for a family. That said, not all trees produce worms. Historically, the practice was common in native environments where the worms typically appear, but they don’t always appear on trees outside their native range.

Where the trees appear, fishermen use them for bait to catch catfish, bream, perch, largemouth bass, and several other species. But if you can't find caterpillars on a catalpa tree, you can purchase frozen worms through Catawba Gold for thawing and use as bait. There's currently an active U.S. patent protecting a method that preserves live catalpa larva for fishing bait; it's been on file since 2008, proof that people recognize the value in selling catalpa worms.