One of our readers recently sent us this message,”I love catawba worms and can’t wait for them each season. I understand the life cycle but have recently found something lethal to my worms. I’m noticing that there are “eggs”, white in color, attached by a clear, viscous, sticky fluid, to the backs of the catawba worms. Within a few days, the worms are dead. These “eggs” have spread onto my other trees/worms. I will attempt to include a photo. Any help in identifying and eradicating will be greatly appreciated.”
In this first photograph we can see two catawba worms. We can’t see the “eggs” our reader mentioned, but he sent another photograph that shows more detail. In this second photograph we can see the white “eggs” attached to the catawba worm:
Catawba worms (also known as catalpa worms since the words “catawba” and “catalpa” are interchangeable) are not actually worms, they are caterpillars. These sphinx moth larvae have a special relationship with catawba trees (a.k.a. catalpa trees) since these trees are their only food source. Some people with catawba trees hate the accompanying caterpillars because they worry about the health of their trees, but the trees can actually withstand a lot. Others, like this reader, enjoy having the caterpillars around, and some even collect them to use as fishing bait.
So, what are the “eggs” that our reader noticed on the caterpillars? We don’t think these are eggs. We believe that these small white attachments are the cocoons of parasitic wasps. Female wasps deposit their eggs inside the body of catawba worms. When the eggs hatch, the larvae feed on the worm’s insides. When the larvae are ready to pupate, they eat their way out of the worm and spin tiny cocoons that attach to the worm’s back. The catawba worm usually survives through this whole process, but dies once the wasps emerge from the cocoons. Since many people consider catawba worms pests, these wasps are actually thought to be beneficial. We don’t know how our reader can prevent his caterpillars from experiencing this brutal demise.
To wrap up, a reader reached out to us because his catawba worms are covered in white “eggs”. These are not actually eggs, but cocoons of parasitic wasps.