Dear Tara,

When you think of the Jurassic Period, you might think of dinosaurs, but all kinds of insects, including praying mantises, roamed the Earth back then, too.

Some of the mantises died and fossilized into rock and amber, which helped to preserve them for hundreds of millions of years. As scientists uncover these fossils in modern times, they can learn more about the life histories of insects.

That’s what I found out from my friend Elizabeth Murray, an entomologist at Washington State University, who is very curious about the diversity of insects on our planet.

Elizabeth Murray

She said that in addition to fossils, scientists will sometimes study insects’ DNA, or their genetic material, to learn about how the insects evolved and any ancestors they might have in common.

If you’re like me, you might be surprised to learn that mantises share a common ancestor with another well-known insect.

“We have pieces of evidence that come together and show that cockroaches and mantises are most closely related,” Murray said. “They had a common ancestor that maybe even looked like a mix of both insects.”

Like a lot of insects, cockroaches and mantises both have six legs and three main body segments. They not only share a genetic history but also lay their eggs in a similar way. Both cockroaches and mantises make a special kind of case to protect their eggs.

The ability to build a tough egg case, or what scientists call an ootheca, helps give the insects an advantage as they protect their tiny eggs from dangers like parasites, predators or weather.

Over hundreds of millions of years, the traits and abilities that help different insects survive have been passed down from parents to their offspring.

Murray reminded me that when we talk about how an insect evolves, we are talking about all of these changes that occur in a species through millions of generations.

Scientists are still learning more about the history of praying mantises and even discovering species that lived in the past.

Just last year, researchers reported their findings of a fossil that helped them identify a previously unknown species of praying mantis. This mantis lived about 100 million years ago in the Late Cretaceous period.

Using modern imaging tools and computer models, scientists can help pinpoint differences and similarities between species that existed millions of years ago and the species that exist now. It helps put together a better picture of the insects’ family tree.

It’s a pretty big tree, too. Murray told me that there are at least a couple million known insect species, but there are some estimates that there might be 10 million insect species on our planet.

Maybe one day you can study to be an entomologist and help us learn more about different insect species. The next time you see a cockroach or a praying mantis, think about how they share a common ancestor—and as always, keep asking great questions.

Dr. Universe