Catalpa Sphinx Moth

Written by Madison Roberts, a Reflection Riding Nursery and Botanical Apprentice

Recently in the Jump Field, where a new monarch waystation has been planted, we spotted a tree covered with caterpillars. This tree is the catalpa, Catalpa bignonioides, which is the host plant for the catalpa sphinx moth, Ceratomia catalpae. Commonly called catalpa worms, these native caterpillars are a hornworm species that have a long horn at the abdomen. The caterpillars start off tiny and pale, but grow up to three inches long. They can either be white with black spots, black on top and pale yellow underneath, or intermediately marked. Once catalpa worms mature, they dig a few inches into the soil under the catalpa tree to pupate; there is no cocoon for these caterpillars. They emerge in March or April and fly through October as brown moths. Catalpa worms are noticeable from May through November and lay 100 to 1,000 eggs at a time. 

The catalpa sphinx moth is a boom-and-bust species, similar to cicadas. They can be absent in an area for years then suddenly densely populate the area. The caterpillars can defoliate catalpa trees during outbreak years and can be considered pests; however, since the catalpa worms are native, they have many natural predators, such as the giant strong-nosed stink bug, Alcaeorrhynchus grandis, and various wasp and fly parasites, for pest control.

These caterpillars are part of the food web that helps other insects complete their life cycles. Birds benefit from catalpa worms, because many birds need soft bodied insects to feed their young. Humans can even benefit from these caterpillars, as they are excellent bait for largemouth bass and catfish, and they can be frozen to be used as bait. Plus, since the catalpa sphinx moth is the only species of sphinx moth that feeds on catalpa, sighting a variety of catalpa worms is truly an exciting experience.

A healthy catalpa tree can withstand complete defoliation by catalpa worms and will often push out a second set of leaves if defoliation happens early in the season. The catalpa tree is available for purchase in the Reflection Riding Native Plant Nursery and can serve as a host plant for this species to promote biodiversity for the ecosystem in your green space.