My son told me something I didn’t know. I thought all little insects had to go through a resting stage to become adult insects. He learned in school that some insects don’t ever become a pupa; they just grow up without that step. Is that right? B.P., Ayer, MA 

Ants do have a pupal stage, though not all insects do.

It’s true that not all insects have a pupal stage. Insect groups that have what we call simple metamorphosis do not go through the dramatic change in form from larval stage to adult insect that butterflies do. Some examples of insects with simple metamorphosis (and without a pupal stage) are cockroaches, crickets, and bed bugs. In these groups, the newly hatched insect is usually called a nymph and it looks like a miniature form of the adult insect that it will become. It grows in size by shedding its outer skin periodically. After its final molt to adult, it doesn’t look much different, except that it is larger and may have added wings and reproductive organs.

In the insect groups with complete metamorphosis (and a pupal stage), the young are very different in appearance from the adult insect they will become. The newly hatched insect is usually called a larva or a caterpillar, it’s often wormlike, maybe legless. Consider a maggot, the larval form of a fly. After the maggot grows as big as it’s going to get, it enters the pupal stage where major changes take place that turn it into a winged fly. Some other insect groups with a transforming pupal stage are butterflies, ants, wasps, and beetles.

The Amazing Insect Pupa

The pupal stage usually takes place in a silken cocoon or some kind of a protective case. Most pupae (pronounced pew-pee) are quiet, and don’t move around. Inside its last larval skin, the insect is changing form, growing wings and legs, and developing sexual organs. A mosquito pupa, aptly called a “tumbler,” is one of the few insect pupae that is active.

The length of the pupal stage varies but is usually only a few days. Usually we don’t even see it happening. The adult fly, or butterfly, or beetle, or yellowjacket, breaks out of the pupal case to face the world in a completely different form.

Sometimes we don’t even associate the larval form with the adult insect that it becomes. For example, those large white grubs that we find in the garden soil are the larval form of the big May or June beetles that fly to our porch lights. Amazingly, they’re the same insect, but they couldn’t perform that magic without the pupal stage.

By ASU Ask A Biologist [CC BY-SA 3.0], via Wikimedia Commons

Stay up-to-date with Colonial Pest’s email newsletter!