MARCH
1999

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

03-11-99

Tobacco Hornworms are Insect Version of Laboratory White Rats

Many species of insects play valuable roles in laboratory research. Cockroaches, grain weevils and several species of flies are easily reared under laboratory conditions. So, these insects frequently serve as experimental animals for studies ranging from traditional genetics and population dynamics to the most modern aspects of molecular biology.

And that's not all. Insects are wonderful teaching tools. For all levels of classroom education-kindergarten to graduate school-insects are the laboratory animals of choice.

One of the most widely used insect species in both the research and teaching laboratory is the tobacco hornworm. Most people recognize the adult of the tobacco hornworm, or the very similar tomato hornworm, as a moth-a rather large moth known as a hawkmoth, hummingbird moth or a sphinx moth.

These are just different common names for a whole group of similar moths. There are more than 100 species of these moths in North America. The name hawkmoth comes from the speed with which the insect flies. In fact, the tomato hornworm is one of the fastest insect fliers, reaching speeds of more than 30 mph.

It is also called a hummingbird moth because-like its bird namesake-it feeds on nectar from flowers, using a long, coiled tongue called a proboscis. Like the hummingbird, it also can fly backward as it moves from flower to flower in search of a sugar fix.

The term sphinx moth is a reference to the habit of the caterpillars that sometimes rear up an Egyptian “sphinx-like" position when disturbed. Such a menacing habit is thought to ward off potential predators that are having thoughts of a caterpillar meal!

While scientists and teachers are willingly raising these insects, gardeners and farmers are trying not to have them around. You see, the tomato hornworm and the tobacco hornworm are names of the immature forms that can be destructive to tomato and tobacco plants. 

The name for the caterpillar is based on the presence of a rather prominent horn on the posterior of the worm. There appears to be no function for the horn other than to suggest that the insect might sting. Apparently, the charade works for it is a common belief that these caterpillars can sting if picked up.

While hornworms are the bane of many home gardeners who keep tomato plants, they are the delight of any brave youngster who discovers them. There is just something about a large green worm with white markings and round “port holes" on each segment that is intriguing. So intriguing, in fact, that some scientists admit to getting a start in biology by observing these insects.

Hornworms also have played prominent roles in movies, including “Silence of the Lambs" where a hornworm pupa was used as the murder weapon. Also, a memorable scene in “Fried Green Tomatoes" shows farm laborers picking tobacco hornworms from the plants in a practice that was common, before the widespread use of insecticides, to kill unwanted pest insects.

In spite of the pest status of the insect in the wild, it is a pampered animal in the research scientist's laboratory. Here, the insect is given the utmost care of a specially prepared diet of the finest ingredients and just the right temperature and humidity. Proving once again that beauty is in the eyes of the beholder. Even if the creature is a common, old hornworm!

 

Writer: Tom Turpin
Editor: Olivia Maddox