Bug of the Week

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.

manduca-larva-largeBy 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?

Often when you see an insect, only one life stage is present.


That wasn't true with the leaf-footed bugs we spotted today. There's an adult on the right. It has full wings and big flaps on its hind legs, which gives it the name "leaf-footed bug." On the left is a large nymph with smaller flaps and stubby wing pads. So, what is the smaller orange insect?


Turns out that is a small leaf-footed bug nymph. Isn't it amazing how different it looks from the adult. It doesn't have flaps on its legs at all.

The adult looks like it is standing over the nymph and protecting it. A little research reveals that leaf-footed bugs are an example of insects that exhibit parental care. In fact, when scientists removed leaf-footed bug adults from their young and placed them on a nearby plant, the adult bugs flew back to the nymphs and stayed with them.

In case you were wondering, these leaf-footed bugs are feeding on the fruit of a datura or moonflower plant.

If you are interested in learning more, here's a .pdf of a Scientific American article about parental care in insects (hosted at Colorado). Very cool!

Manduca rustica caterpillars usually feed high up in the desert willow tree and are hard to observe.

1-Manduca-rustica-caterpillar- 338This week one chose a low branch that was within easy reach.


It was eating the willow leaves from tip to base.



Can you see its legs, which is uses to hold onto the leaf? What about the antenna and eye, which are right by the mandibles?

The cream-colored oval behind the head is a spiracle. Spiracles are opening that allow air to pass into and out of the insect.

Have you ever watched a caterpillar eat a leaf? What kind was it?