The Catalpa Tree and Its Caterpillars

There are two species of catalpa trees in North America, and they are both natives. They can be recognized by their large, heart-shaped, sharp-pointed leaves, showy white or yellow flowers, and long fruits that resemble a slender bean pod. Also sometimes spelled "catawba," the catalpa tree is the sole source of food for the sphinx moth larva, which turns into a distinctive caterpillar with yellow and black markings. If you are considering planting this beautiful and popular tree in your landscape, learn more here:

Naturalized Specimens

Catalpa on Lake Dam

Steve Nix

Catalpa speciosa, also called the northern catalpa or cigar tree, features a loose oval leaf shape and can grow up to 50 feet tall in most urban locations—occasionally up to 90 feet under optimum conditions. This large-leaved tree spreads 50 feet and tolerates hot, dry weather, but leaves may scorch and some drop from the tree in very dry summers. The leaves of speciosa grow opposite, or in whorls, to each other, meaning there are a pair of leaves on each node, and growth is opposite to each other, rather than alternate.

Catalpa bignonioides, or southern Catalpa because they are native to the southern U.S., is somewhat smaller, reaching only about 30 to 40 feet tall. Its leaves are also arranged opposite to each other. A sunny exposure and a well-drained, moist, rich soil is preferred for optimal growth, but the tree will tolerate a range of soils, from acid to calcareous. 

 

Tough and Adaptable

Catalpa Leaf and Fruit

Steve Nix

Catalpa is a tough, adaptable tree that has a moderately long life—60 years or so—but trunks on very large trees often contain rot. It is also used as a land reclamation tree because it will grow successfully in those places where air pollution, poor drainage, compacted soil, and/or drought can become a problem for other species. It produces lots of shade and is a fast grower.

The largest living catalpa tree is located on the lawn of the Michigan State Capitol, planted at the time the Capitol was dedicated in 1873. The oldest known living catalpa tree is actually in the United Kingdom, a 150-year-old specimen in the Minster graveyard of St. Mary's Butts in the town of Reading, Berkshire.

Young catalpa trees are beautiful green standouts with giant green leaves that can sometimes be confused with tung trees and royal paulownia in the southern U.S. Catalpa seedlings are somewhat available, but you may have to go out of your region to find the tree. Catawba's USDA hardiness zones are 5 through 9A, and ​it grows from coast to coast.

Planting Considerations

Catalpa Tree

Steve Nix

Catalpa growth is rapid at first but slows down with age as the crown begins to round out and the tree increases in spread. The main ornamental feature is flower panicles of white with yellow and purple markings that are produced in spring and early summer, depending on the particular tree.

Leaves fall throughout the summer in USDA hardiness zone 8, making a mess, and the tree looks ragged with yellow leaves in late summer. Flowers make somewhat of a slimy mess for a short period when they drop on a sidewalk but are no problem falling into shrubs or onto ground covers or turf. Spent bean pods also make a mess and can look a bit coarse alongside the green pods.

Catalpa bark is thin and easily damaged from mechanical impact. The limbs will droop as the tree grows and will require pruning for vehicular or pedestrian clearance beneath the canopy. Pruning is also necessary for the tree to develop a strong structure. The limbs are resistant to breaking and very stout.

The tree is useful in areas where quick growth is desired, but there are better, more durable trees available for street and parking lot plantings. Sixty-year-old trees in Williamsburg, Virginia have three to four-foot-diameter trunks and are 40 feet tall. Catalpa can be invasive and often escapes cultivation and invades surrounding woodlands.

Bean-Pod Shaped Fruit

Catalpa With Fruit

Steve Nix

The catalpa is sometimes called the Indian bean tree for its production of a distinctive fruit that resembles long, thin bean pods that can grow up to two feet long. The old pod shells are persistent on limbs but will eventually drop. Still, the pod is attractive and adds visual interest to an ornamental specimen.

Sphinx Moth

Catalpa Worm Damaged Tree

Steve Nix

Like most trees, the catalpa is susceptible to insect infestations. In fact, it is the sole source of food for the catalpa sphinx moth larva, the larval stage of Ceratomia catalpae. When first hatched, these larvae are very pale in color, but become darker as they age. The yellowing caterpillars will usually have a dark, black stripe down their back along with black dots along their sides.

They grow to a length of about two inches and feed on the leaves of the Northern catalpa and, more commonly, the Southern catalpa. The fully developed caterpillar has a conspicuous black spine or horn on the back at the insect's rear. 

Owners might be alarmed at what can be a sizable infestation, but even if the caterpillars defoliate the tree completely, it usually causes no adverse consequences to the health of its host, which bounces back to leaf out the following year.

Prized Bait

Bucket of Catalpa Worms

Steve Nix

While the average homeowner might want to protect their catalpas from damage, in some areas of the country they are planted to deliberately attract the larvae. Prized as fish bait because their tough texture makes for easy hooking, the worms also ooze a bright fluorescent green fluid that smells sweet to the surrounding fish. 

Once harvested, the catalpa worms can be preserved alive by placing them in cornmeal packed in an airtight container and then frozen. When the container is opened and the worms are removed from the meal, they thaw and become active.

Another method of preserving the caterpillar for future use is "pickling" them in a baby food jar filled with corn syrup. The jar should be immediately stored in a refrigerator and has an indefinite shelf life.