I’d been waiting for them to appear since the first leaves of the catalpa tree began to sprout earlier in the season. I finally noticed their handiwork on the 18th of June. The large, long-stalked, heart-shaped leaves of the tree were becoming mere skeletons (top photo, 6/18).
When I discovered the caterpillars they were about 1/2” long and feeding gregariously with their siblings. They had the potential of reaching 3” in length. They were the larvae of the catalpa sphinx moth (Ceratomia catalpae).
Most sphinx moths feed alone (picture a tobacco or tomato hornworm, both sphinx moths). Catalpa worms, as they’re usually referred to, feed in clusters during their first two or three instars. That’s perhaps due to the adults laying of tiny, pearly eggs in clusters, sometimes a couple of hundred per cluster. In their final larval stages the caterpillars spread out and feed, more or less, singly.
Catalpa worms are a favorite bait of southern fishermen. You can collect them yourself. You can buy them online. You can buy lures or flies which mimic the caterpillar. The bait, live or artificial, is good for anything from catfish to bluegills to largemouth bass.
Though fish will gobble up the caterpillars, birds seem to find them distasteful. The catalpa leaves are supposedly toxic. In this case, you are what you eat.
The caterpillars took 9 days to completely devour all of the leaves on the catalpa tree in question, which is located on the Dinosaur Trail here at the museum. They even started to eat the veins of the leaves. Some of the caterpillars looked to be in their final stage, or instar, and ready to pupate, though a bit early. However, many of the larvae were not prepared for pupation.
The caterpillars all crawled down from the tree and along the ground looking for more trees to climb and leaves to eat. I found them on palm fronds, horsetail (Equisetum), and other nearby vegetation. The problem? Catalpa sphinx moths only eat catalpa. They had literally eaten themselves out of leaf and tree.
Some of the caterpillars starved, some were stepped upon as they attempted to cross the path, and others are hopefully now under the soil pupating.
All that’s left is one catalpa tree devoid of leaves.