A bug’s life: understanding insect transformation

Insect expert Wizzie Brown has a guide for understanding the different types of insect life cycles.

By Laura RiceSeptember 29, 2023 9:13 am, , ,

Texas Standard’s go-to insect expert, Texas A&M AgriLife Extension Service Specialist Wizzie Brown, often focuses her regular segments on specific critters you’re likely to find around the state. Some are strange, some are stinky, some are seriously what you don’t want to see in your yard.

Many times, our interactions are with the adult versions of these insects. But some are more likely to get our attention – or bother us – in earlier stages of life.

There are two basic categories for insect life cycles.

An illustration of the two primary types of life cycles.Incomplete or simple metamorphosis (AKA paurometabolous)

“They essentially have three life stages, so they’re going to have an egg stage. They have several nymphs instars and then they have the adult stage,” Brown says.

An instar, she says, is essentially the animal between two molds.

And, like the name implies, the change between an insect in this category isn’t very significant.

“The nymphs look very similar to the adults in the way that they’re built and structured, but they don’t have fully developed wings,” Brown says.

Other insects, of course, won’t ever develop wings. An example would be a bed bug.

Within this category of incomplete metamorphosis, there are two subsets. The first is ametabolous, which essentially means no metamorphosis. This, Brown says, describes some very primitive insects like springtails and silverfish.

“The nymphs look exactly like the adults. It’s just that they’re smaller,” Brown says.

The other subset is hemimetabolous. The special thing about the insects in this category is that the nymphal stage is aquatic.

“So these would be things like dragonflies and damselflies,” Brown says.

The adults would lay an egg on or near the water and, when it hatches, the nymph would be a water predator.

“But they have to somehow go from that aquatic stage to land,” Brown says. “And so they have this kind of in-between stage that’s called a subimago. It’s essentially where the nymph is going to emerge out of the water and it crawls up on a plant or a rock or something like that. And that allows that adult then to emerge out.”

Complete metamorphosis (AKA homometablolous)

The other type of insect life cycle has four life stages instead of just three. Both start with an egg stage, but the complete metamorphosis cycle then moves to a larval stage, with the potential for several instars, and then the pupal stage before the adult stage.

You are probably familiar with this without quite knowing that you are. That’s because some larvae have names that are more specific.

“So if we talk about caterpillars, those turn into butterflies and moths. If we talk about maggots, those will turn into flies. If we talk about grub worms, those will turn into beetles,” Brown says.

Unlike in the incomplete metamorphosis, insects in this category can look very different from one stage to another. Brown says this can be very valuable to keep in mind when considering beneficial insects.

“It’s important if you want to have something like a butterfly garden to know what the caterpillars and the butterflies look like, because a lot of times if people are inexperienced, they may end up killing the larvae because they don’t know what it is and it’s feeding on their plants,” Brown says.

The length of an insect transformation

Brown says exactly how long it might take for an insect to grow from egg to adult is dependent on several factors.

“The number of instars that an insect can have can vary widely, so you can have anywhere from like three instars to 17 instars,” Brown says.

Other factors are environmental and biological.

“Like if you think about a housefly in summer in Texas, that takes about 5 to 7 days to go from egg to adult when it’s really warm out,” Brown says. “But then we also have insects like periodical cicadas in the Midwest where it takes anywhere from 13 to 21 years from them to go from egg to adult.”

Do you have a bug question for Wizzie Brown? Drop us a line, and we’ll pass it along.

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