A reader asked us a couple of days ago why there are no longer Catawba worms on her Catalpa trees (or Catalpa worms on her Catawba trees – “Catalpa” and “Catawba” are interchangeable). Catawba worms make excellent fishing bait, so the reader was keen to find out how to attract them back to her trees. Since she gave no information about her circumstances, it’s of course very difficult to say why the Catawba worms left, and for similar reasons it is hard to say how to get them back. (Obviously, the two questions are related.) Even in the absence of specific information, we can still supply some general information about attracting Catawba worms to Catalpa trees, and what keeps them away.
We should begin by saying that Catawba worms, which are the larval form of sphinx moths, making them a type of caterpillar, are very discerning eaters – they only eat Catalpa trees, or technically the leaves of Catalpa trees, as we explain in our article about Catawba worms and what they eat. We assume our reader knows this and has Catalpa trees in her yard, and indeed this is implied since she once enjoyed the company of Cawtawba worms, but we thought it was worth mentioning because she only referred to “trees” in her email. If her trees have been replaced, or if the number of Catalpa trees has decreased, then this would have a depressing impact on the Catawba worm population, and it would reduce their numbers too. (Ha.) Since Catawba worms exclusively feed on the leaves of Catalpa trees, the best way to attract them is to have several healthy and leafy trees in one’s yard. Again, we have no idea what our reader’s situation is, but if her Catalpa trees aren’t in good health, this could certainly disincline the caterpillars from settling on her trees. (In general, Catawba worms don’t harm the trees they feed on – they merely defoliate them – but after years of serious infestations, they can weaken and even kill a Catalpa tree. So, if our reader experienced particularly bountiful years of caterpillars in the past, perhaps this has finally taken a toll on her trees.)
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If the trees appear to be healthy, there are a couple of other factors that might be impacting our reader’s Catawba worm situation. First, and as we explain in our article about where to find Catalpa worms, the number of worms you find depends on the time of year you are looking for them. If a long, cold winter pushes the start of spring back, this could delay the emergence Catawba worms, which largely follow the rhythms of the trees’ initial blooming and subsequent growth (because they eat the trees leaves, which obviously need to grow before they can be eaten). So, perhaps the Catawba worms in our reader’s part of the country (wherever that may be) have merely been delayed in coming out. Second, Catawba worms have a number of natural predators, which can wipe out several hundred caterpillars (often the entire population of a tree) with surprising swiftness. One of these predators are wasps, which lay their white eggs inside of the skin of Catalpa worms, but there are additional predators as well, including other types of insects and various birds. Thus, even with perfectly healthy trees and a normal spring, Catawba worms might not be found.
As we have stated repeatedly, we don’t know why our reader in particular can’t find Catawba worms. Perhaps she is dealing with a unique situation, and thus none of what we say above applies to her specific circumstances. However, what we say is true in general, and if you are looking to attract Catawba worms, you might be working against tree health, the weather, and natural predators.
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