Beautiful catalpa sphinx caterpillars are among the largest caterpillars found in the DMV.
Adult catalpa sphinx moths blend in with substrates like the brown bark of trees. Thanks to Wayne Owen for the use of his great image.
Several members of the moth family called the Sphingidae are known as sphinx moths owing to the defensive behavior of larvae which rear upright presenting a visage reminiscent of the lion-headed Great Sphinx of Gaza. Often accompanying this display is a vomitous regurgitation of partially digested catalpa leaves meant to deter would be predators. This performance certainly would deter me from eating one.
The female sphinx moth lays batches of eggs often numbering in the hundreds on the leaves of both northern and southern catalpa trees. After hatching, larvae feed gregariously for the first several instars of their life before feeding singularly in their latter stages. Fully developed larvae wander from the plant to the soil where they form a pupa. Two or three generations are present annually throughout the range of the moth and winter is spent as a pupa in the soil near its catalpa host. Under ideal conditions for survival of adults and larvae, large populations may defoliate portions of catalpa trees.
Catalpa trees are host to the larvae of the catalpa sphinx moth. These larvae are one of the largest and most striking of all caterpillars in North America. Early stages are a chummy lot and feed gregariously. Their feeding generates waste called frass that piles up on leaves and the ground below. Watch as this one nibbles off the tip of a leaf. Ah, but like other sphinx moth caterpillars they are attacked by small parasitoid Cotesia wasps. After completing development inside the caterpillar, wasp larvae emerge through the caterpillar’s skin and spin small silken cocoons on the caterpillar’s surface. You may have seen Cotesia cocoons on a hornworm caterpillar on your tomatoes. Parasitoids like this make me glad I’m not a caterpillar.
Small Cotesia wasp larvae develop inside catalpa sphinx caterpillars before emerging through the cuticle and spinning white cocoons on the surface of their hapless host.
As with many caterpillars and other herbivorous insects, when populations become locally dense, natural enemies often arrive to take advantage of the bounty of fresh meat. A small parasitoid braconid wasp, Cotesia congregata, attacks and kills larvae of several species of caterpillars including tobacco and tomato hornworms in addition to those of the catalpa sphinx. We met clever Cotesia parasitoids attacking larvae of saddleback caterpillars in a previous episode. Check out that episode to see these alien-like creatures emerging from the skin of their host - truly creepy. Another moniker for caterpillars in the family Sphingidae is horn worm. One legend has it that the prodigious horn on its rear end is poisonous. Well, I tempted fate with one of the large catalpa sphinx caterpillars and found the horn to be rather tickly but certainly not capable of delivering any type of venom.
Can this horn on the rearend of a catalpa sphinx caterpillar deliver an awful sting? Nope.
Acknowledgements
Bug of the Week thanks eagle eyed Erika and the wonderful Cylburn Arboretum for allowing me to visit their catalpa sphinx caterpillars that inspired this story. The fact-filled “Caterpillars of Eastern North America” by David Wagner was used a reference for this story. Special thanks to Wayne Owens for allowing the use of his image of the catalpa sphinx through Creative Commons.