KNOXVILLE, Tenn. (WATE) — The Brood X cicadas have been popping out for a couple of weeks, but not everyone has seen them in their trees or plants.

Experts said everyone won’t see them, even if they live in the geographical zone where the insects are expected to pop up.

Dr. Frank Hale, an entomologist with the University of Tennessee Extension, said there are some factors in play that could determine whether cicadas will show up in your yard.

“They’re looking for a twig, usually what, a pencil size in diameter, maybe even smaller, to lay their eggs,” Hale said.

That sounds pretty much like most trees and plants in East Tennessee.

Hale said the insects do prefer some types of plants and trees over others.

“They get in a lot of hardwood, or deciduous, you know, deciduous means they’re trees that leave their leaves in the fall. They like a lot of those types of trees to lay their eggs in,” Hale said.

He said they’ll get into hackberry trees, cherry trees, apple trees–a lot of fruit trees; and elms.

In East Tennessee, there are a lot of trees and plants cicadas will enjoy, Hale said.

However, another factor comes into play: the past.

Hale said these insects are thousands of generations old, and they need trees.

If over the last few decades, or centuries, a lot of lands have been cleared and trees were never replaced or the area was heavily developed, cicadas probably won’t be around.

“You know, you might have big farmland and they took all the woods out. So, there’s just not as many of them there anymore. They have to have the trees. So, they have to have the host plants,” Hale said.

Plus, Hale said, cicadas don’t move a lot.

He said when they are underground, they barely move at all.

When they are adults, he said, they might move about a mile or so, flying.

Plus, he said, after the females lay the eggs and they hatch, the babies simply fall directly underneath from where they were.

“Slowly moving around over thousands of years, yeah, over time, they move around a little bit. But, within our lifetime, they’re not going to much at all,” Hale said.

That means they could, over a lot of time, move into other areas that have the trees and plants they like.

So, said a good rule of thumb to know if you will see (and hear) them this year, is if you saw them 17 years ago.

Of course, that is if you’re still living or working in the same place you did 17 years ago.

Another tidbit Hale added, was that if you haven’t seen the cicadas yet, and they have been in your area before, then it could just be the weather delaying their emergence.

“If you’re on the north side or a hillside that faces north, it’s going to get less sunlight, and the soil is going to be cooler and those cicadas might come out a little later,” Hale said.

Hale said that in the past, mapping cicadas was difficult.

Scientists relied on checking in with local officials and other scientists in the area to see if they’ve seen or heard any cicadas.

Now, as more technology becomes available, Hale said it’s going to be easy for everyone to help map out where the cicadas will emerge.

He said he likes using the app ‘Cicada Safari.‘ He said anyone can post a picture of the cicadas in their yard, and the app will pin that location.