We decided to title this article with more or less the exact wording of an email we recently received from a reader. She reported that her “catalpa worms have white spikey things all over them,” and she is wondering what is going on. Something is clearly amiss with her Catawba worms. (For the record, Catalpa worms are Catawba worms and vice versa, as the words “Catalpa” and “Catawba” are interchangeable). The reader asked no additional questions, so we will focus only on the white spiky things on the Catalpa worms. We won’t worry about general matters of identification, presuming our reader is definitely dealing with Catawba worms, and we also won’t worry about ways to rectify the problem, which may not be possible anyway.
For those who don’t know anything about Catalpa worms, we should mention that they actually aren’t worms. Rather, they are caterpillars. (More precisely, they are the larval form of Catalpa Sphinx moths, or Ceratomia catalpae, a common type of hawk moth.) Catawba worms are on most people’s radar because they make excellent fish bait. In fact, many people plant Catalpa/Catawba trees precisely to attract the caterpillars, and if the caterpillars don’t come, or they cease to come after years of faithful infestation, this can cause the tree owner plenty of distress. (We have already answered two questions this summer about why Catawba worms leave trees and how to attract Catawba to your Catalpa trees.)
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As for our reader’s more specific question, we are fairly sure we know what she is dealing with: her Catalpa worms are probably being attacked by wasps, one of the caterpillars’ natural predators. The wasps attack in a fairly gruesome way, with the females laying their eggs inside the caterpillar. The wasp larvae hatch inside the caterpillar, consuming the host’s interior until they emerge through the skin and spin white cocoons. We suspect that the white spikes that our reader refers to are these white cocoons, which on the body of a Catalpa worm look like this:
We have actually written about this phenomenon before, although it was part of a broader discussion about (what were believed to be) white eggs on Catalpa worms.
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We can’t be entirely certain what our reader found, but it seems fairly likely that she is observing Catalpa worms that have been attacked by wasps. We don’t know what else could account for the “white spiky things” on the caterpillars’ body. If our reader is collecting Catawba worms as fish bait, hopefully the white spiky things haven’t spread among the whole population, as the caterpillars that are attacked by wasps are, not surprisingly, unable to survive the larvae-growing-inside-them ordeal. Regardless, wasps are probably to blame, no matter how far their destruction has spread.