It isn’t unusual to find tobacco hornworm caterpillars on the datura plant.
What is unusual is to find one with such a long “horn.” It is likely that it recently hatched from an egg.
Probably most of you know that insects need to shed their exoskeleton or outer “skin” in order to grow (as well as the linings of the breathing tubes and parts of their digestive system). When an immature insect sheds its exoskeleton or molts, it is said to enter the next “instar.” The word instar is Latin and it means likeness or counterpart. The caterpillar above would be in its first instar.
Tobacco hornworm caterpillars generally go through 5 instars, but that number can vary with environmental conditions.
By the time it is ready to pupate, the “horn” will be much smaller in proportion to the rest of the body.
Before it pupates, the tobacco hornworm caterpillar will leave the plant and look for a place to burrow into the soil, as shown in this time lapse video.
Before long an adult moth will emerge and the cycle will continue.
Why do you think the first instar caterpillar is “rearing up” with its head away from the plant? Any ideas?
We found this brave caterpillar is feeding on a jalapeno pepper plant.
It is the tobacco hornworm, Manduca sexta, often confused with the tomato hornworm (Manduca quinquemaculata). The tobacco hornworm has straight white lines on its sides. The tomato hornworm has V-shaped markings.
It gets its name “hornworm” from the thorn-like projection at the rear of the caterpillar. The horn is not dangerous in any way. The caterpillars are perfectly harmless, except to plants.
Notice its three pairs of true legs right next to the head. The rest are fleshy prolegs.
When it finishes eating, the larva will drop off the plant and dig into the soil to pupate. The adult moth is called a hawkmoth or sphinx moth. It flies at night and isn’t seen much during the day.
Tobacco hornworms are easy to raise and are great subjects for science activities with children.
The University of Arizona’s Manduca Project website has a wealth of information about the life cycle, techniques for rearing Manduca, lesson plans (including cool science projects) and videos. Go check it out!