Ask Dr. Universe: Ladybugs undergo complete metamorphosis as they mature

Dr. Universe: What is the life cycle of a ladybug? – Rachel, 6, Virginia

Dear Rachel,

Every spring, I see spiny bugs that look like tiny alligators. They spend all day chomping up other insects outside my window.

I asked my friend Rich Zack about them. He’s an insect scientist at Washington State University.

He told me those spiky gobblers are immature ladybugs.

The ladybug life cycle includes complete metamorphosis. They undergo big body changes to become adults. An insect that does that is holometabolous.

“Millions of years ago, holometabolous insects split up their duties between the immatures and the adults,” Zack said. “An immature’s job is to feed. An adult’s job is to mate.”

There are four stages in this life cycle: egg, larva, pupa and adult.

A ladybug starts out as an egg. They’re yellow or orange. They look like fat grains of rice. You might find them on the underside of leaves.

After a few days, the eggs hatch. A spiny larva comes out. Its job is to eat and grow.

First, it chows down on extra eggs its mother left behind. A particularly peckish larva might also eat its siblings–especially the small or slow ones. Then it starts snacking on nearby soft-bodied insects.

As it grows, its tough outer skin, or cuticle, gets too tight. The larva pops the skin open and climbs out. It has a new, bigger cuticle ready to expand and harden to fit its body.

The larva will molt like this a few times. The time between molts is called an instar.

After a few weeks, a ladybug larva is ready to transform into an adult. It sheds its cuticle one last time. But this time it stays inside. That’s now a pupal case.

The pupal case is hard. It sticks firmly to a leaf or other surface. Inside, the larva’s body breaks down. It reorganizes into an adult body.

After about a week, an adult ladybug comes out.

Zack told me that most insects go through a big change like that. About a third of insects go through a partial metamorphosis instead. Those insects are hemimetabolous.

They have three stages: egg, nymph and adult.

Since they don’t undergo a big change, the immature nymphs look a lot like the adults. They’re just missing wings and working reproductive parts. They’ll get those at their final molt.

The least common life cycle has no metamorphosis at all. Those insects are ametabolous. The juveniles look exactly like the adult, just smaller. They never get wings.

Ametabolous insects are so well-adapted that they haven’t changed much for millions of years. The ancestors of all insects were ametabolous.

Complete metamorphosis–like ladybugs undergo–is the newest insect life cycle.

It’s possible it evolved so the juveniles and adults don’t compete. Or maybe it happened that way to make better wings. But it’s still a mystery. It’s wild that so many insects break down and reorganize their bodies just to grow up.

“It’s so complicated and so vulnerable,” Zack said. “We see changes in other animals but nothing like this. It’s just amazing.”

You really can’t beetle an awesome adaptation like that.

Sincerely,

Dr. Universe

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