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By TOM TURPIN
Years ago when I was growing up on a farm in Kansas, my old neighbor had what he lovingly called his fishin’ worm tree.
Back in those days, I didn’t know much about trees, other than some were good for climbing. But I did know the worms I used for fishing were found in the soil. So my neighbor’s name for the tree was a bit confusing.
At least it was until that fateful August day when a friend and I were headed to the creek with fishing poles in hand. Our digging in the dry soil of August had produced no earthworms, so we turned to our seasonal alternative fishing bait: grasshoppers.
On the way to the creek and the old fishing hole, we walked by the neighbor’s house; he suggested we try some of the worms from his worm tree. In his words, “Catfish go for those worms better than any bait I ever used!” So we followed him to a tree with big leaves and long seedpods. There, on the leaves of that tree, were some two-inch-long, black-and- yellow-striped caterpillars. We gathered a couple dozen or so to add to our bait collection.
That was my introduction to the insect known as a catalpa sphinx, just one of a large group of moths known as sphinx moths. The name comes from the fact that the caterpillars strike a pose that reminded people of the Egyptian sphinx, a colossal statue with the body of a lion and the head of a human.
Sphinx moths are also called hummingbird moths. That is because some species are the size of hummingbirds and behave like hummingbirds as they feed on nectar from flowers. The insects are also sometimes called hornworms. This name is based on the fact that the caterpillars of most species have a prominent horn on the rear end of their bodies.
Most gardeners know about hornworm caterpillars because of the tomato hornworm. This insect feeds on tomato plants and is one insect pest that many gardeners encounter on a regular basis.
The catalpa sphinx feeds, as the name suggests, on the foliage of the catalpa tree, which is native to North America. The tree has been widely planted as an ornamental. Two catalpa species – the southern and the northern – are common and can be found today from New York to Kansas. The catalpa is most abundant in the southeastern states.
The caterpillars are sometimes called Catawba worms. That name is based on the Catawba Indian Nation; catalpa is a transliteration of Catawba in the original scientific description of the tree.
In some areas the catalpa is called the fish-bait tree. Apparently what my old neighbor knew and what my friend and I discovered that day in Kansas is that fish really like to eat catalpa worms.
These caterpillars are sold in some fish-bait stores and artificial flies are even tied to mimic them.
Similar to other insect populations, the number of worms present on a catalpa tree can vary from year to year. In addition, some trees seem to be fed on by the worms in most years while other trees in the same area seldom are.
Here’s how the biology of the insect works. The insect spends the winter as a pupa hidden in the soil. The moths emerge in early May in most areas and begin to lay eggs. The female deposits the eggs in a mass that can contain up to 1,000 eggs.
It takes about three weeks for the caterpillars to reach full size. There are three or four generations per year, so larvae can be found into the fall.
There are a number of predators and parasites that feed on the eggs and caterpillars. That is one reason that populations of catalpa worms vary from year to year.
One such parasite is a small wasp that uses her stinger to lay eggs inside the caterpillar. The baby wasps then feed on the innards of the caterpillar. When feeding is complete, the baby wasp chews through the caterpillar skin and spins and attaches a cocoon to its host.
It must be tough being a caterpillar when a comment on life might be: “If a parasite doesn’t get you, then a fisherman will!”
Turpin is professor of entomology at Purdue University.