Hornworms

Hornworm is a name given to the larvae of a group of species known as sphinx moths.  The name comes from the horn like projection found at the back end of the caterpillar.  I found this guy as I checked on the garden on my way to the woods.  This is the Tobacco Hornworm, perhaps my favorite of all caterpillars.  Some of my earliest recollections are of finding caterpillars like this stripping leaves from our garden tomato plants.  If undiscovered by parasite and predators, it is destined to become a Carolina Sphinx moth.

It pulls in its head and legs when disturbed and at a glance, looks very much like a natural part of the tomato plant.  When I was eight years old, I was the kid people called to remove these giant monstrosities from their tomato plants.  I was happy to oblige.  I don’t think they would have appreciated the fact that I took the caterpillars home and raised them to the adult moth stage.  Fortunately for me, we lived in an area where the species was double brooded, which meant that the early caterpillars that I collected transformed to adults without having to go through the winter.  I released the adults in our back yard and am sure they headed for the neighbors garden to lay more eggs.

As I entered the woods, I found a different species of hornworm.  This is the caterpillar of the Laurel Sphinx.  The colors are clear and bright when viewed close up.  At a distance, the caterpillar is almost impossible to see.  Green, yellow and black are the colors of a summer woods and this caterpillar blends right in.

I was especially impressed by the yellow bands around the legs looking like a brightly colored set of spats. 

What at first appeared to be a mottled pattern on the back, turned out to be wounds created by exiting Braconid Wasp larvae.  The caterpillar suffered massive internal injuries inflicted by the feeding wasp larvae and will not live long enough to pupate.

I found a third species of hornworm feeding in a thicket of Virginia Creeper.  This is the caterpillar of the Virginia Creeper Sphinx. 

There turned out to be several of the caterpillars in this patch of Creeper.  Most were hidden beneath the leaves, but this individual was on the move to a new feeding location.  All were this same pale green color which made them easy to spot against the darker green of the Virginia Creeper leaves.

The small head and forward segments ballooning into the large body is a characteristic of this species.  There are many more hornworm species I have yet to encounter, but I felt particularly fortunate to see three in one afternoon. 

Tobacco Hornworm

If you want to attract butterflies and moths, the best strategy is to grow host plants, the plants on which the larvae feed. The primary function of an adult Lepidoptera is to reproduce and the number one attractant is a place to successfully lay eggs. When nectar sources are absent from the host plant location, females will often starve to death laying eggs instead of moving off in search of food. Many moths, such as the giant silkworm moths, don’t even have mouth parts, so are incapable of eating. A garden full of chomping caterpillars is what you need if you want to see the greatest butterfly diversity.

This voracious consumer of tomato plants has got to be familiar to anyone who has ever had a garden. This is the Tobacco Hornworm, Manduca sexta, the larva form of the Carolina Sphinx moth, one of the Hawk Moths. The Tobacco Hornworm is identified by its parallel white stripes and red colored horn. The very similar Tomato Hornworm has a white “V” pattern on its flanks and carries a black horn.

There’s not much in the way of eyes here. In fact, there was no reaction at all to nearby movement or passing shadows. The larva can’t let anything slow its pursuit of nourishment. Like most herbivores, it’s not terribly effective at digesting and extracting nutrients from plant material. As a result, it has to pass a lot of plant material through its body in order to accumulate the energy necessary to complete metamorphosis.

Look at those choppers. The Tobacco Hornworm is so often seen on cultivated plants that many people have forgotten that it is a native species that was here long before we began supplying it with an easily accessible buffet. Members of the plant family Solonaceae are the primary host plants for this moth. Virginia Ground Cherry, an Ohio rarity, fits this category, but is such a small plant that it would take a small patch to grow one larva. Could this be one of the reasons for the rarity of this plant? One hornworm could consume the above ground portion of every Virginia Ground Cherry at Blue Jay Barrens. This would certainly mean trouble for the plant.

Judging by the amount eaten, this pepper plant in my garden is quite edible. Leaves, stems and fruits are all consumed. My guess is that the larva couldn’t consume the fruit as easily as the leaves, so it couldn’t take in enough to keep the body growing. With nothing left but a gnawed pepper fruit, the larva left this plant in search of another. Moving is a risky business since there’s a chance that no new host plant will be found. Fortunately, I planted a whole block of peppers, so the larva quickly found a new plant to devour. My wife loves peppers, so if she voices her displeasure at my letting the Hornworm eat two of our pepper plants, it will be evidence that she does look at this blog.