Catalapa sphinx moth caterpillar, finding a place to pupate underground, 9 August 2026 (photo by Kate St. John)

2 September 2026

For insect novices like me, August is the easiest time of year to find any life phase of the catalpa sphinx moth (Ceratomia catalpae). In August the caterpillars are large and their bodies signal that it’s time to stop eating and start pupating. They drop from the trees and burrow underground to overwinter and pupate. That’s where I found the caterpillar pictured at top in early August.

How did he reach that stage? Here are some of the steps in his transformation.

1. His parents pupated and emerged in April or May. They are well camouflaged in the woods but not as interesting as the last instar.

Adult catalpa sphinx moth (photo from Wikimedia)

2. His mother looked for a catalpa tree and laid her eggs on the undersides of the leaves.

Catalpa sphinx moth eggs (photo by Lacy L. Hyche, Auburn University, Bugwood.org)

3. By June in Pittsburgh northern catalpas (Catalpa speciosa) are in bloom and already have eggs and caterpillars under their leaves.

Northern catalpa in bloom, Schenley Park, 18 June 2016 (photo by Kate St. John)

4. When they hatch the caterpillars a very pale but they do have that distinctive black horn.

Catalpa sphinx moth caterpillars hatching (photo by Lacy L. Hyche, Auburn University, Bugwood.org)

5. In early August in the final (or near final) instar they have yellow sides, a black back and, yes, the black horn.

Catalpa worm, larva of catalpa sphinx moth, Frick Park, 7 Aug 2025 (photo by Kate St. John)

At this point their damage on the catalpa leaves is obvious.

Catalpa whose leaves have been devoured by catalpa worm, Frick Park, 7 Aug 2025 (photo by Kate St. John)

6. The final instar burrows underground and forms a cocoon — which I never see because I don’t go digging for them. The cocoon waits until spring to emerge as an adult.

Catalpha sphinx moth cocoon (photo by Herbert A. ‘Joe’ Pase III, Texas A&M Forest Service, Bugwood.org)

And then the cycle starts over again.

Meanwhile this tree in Schenley Park saw no catalpa sphinx moths this year. It went through its own transformation from flowers in June to long seed pods in August.

Catalpa tree with seed pods, Schenley Park, 19 August 2026 (photo by Kate St. John)