We’ve been hearing it for months: The cicadas are coming. Now, the wait is over.

Leslie Baldacci saw the signs and knew the cicadas were near, but when she woke up Friday morning, she was shocked by the invasion of cicadas swarming the tree in front of her Morgan Park home.

“There are hundreds of them on the tree,” said Baldacci, a former Sun-Times reporter. “They are clustered all over the bark, especially on the sunny side of the tree, and they are covering the grass down at the bottom.”

Baldacci, 69, has spent the last few days preparing for their arrival. She’s been weeding and readying her garden in hopes of avoiding being near them while they take over the next few weeks.

“I’m a gardener and an observer of nature, so I’ve kind of been tracking them and getting everything done ahead of time,” she said. “Yesterday I saw a few cicada shells and some holes in the ground, so I knew they were here. I just didn’t actually see them until my yard service guy pointed them out.”

Periodical cicadas have arrived in the Chicago area for the first time since 2007. This year marks a historic year for cicada emergence, as the breeding group that emerges every 17 years is overlapping with the 13-year breeding group, seen in downstate Illinois. It’s the first time the two broods have overlapped here in 221 years.

The last time the 17-year cicadas were visible in northern Illinois, George W. Bush was president, Rihanna and Jay-Z’s “Umbrella” was topping the charts, and the iPhone was just being brought to market. They won’t emerge in the area again until 2041.

“It’s nature’s creations at their best,” said Stephanie Adams, plant health care leader at the Morton Arboretum, while holding handfuls of cicadas.

The creatures that emerge every 17 years are different from the insects that buzz in the area every year later in the summer. These cicadas are larger with red eyes and delicate, “lacy,” almost transparent, wings.

At the arboretum in Lisle Friday, staff had identified a few “localized areas” where the earliest cicadas have begun to come up from the ground. The arboretum first saw emerging cicadas Monday, staff members said.

While below ground, the nymphs are busy feeding and growing in preparation for their rebirth above ground. Once above ground, they shed their exoskeleton quickly, generally within a few hours. Before they shed their cream-colored exoskeleton, they’re limited in what they can do.

“They’re sitting ducks,” Adams said. “They don’t bite, they don’t sting, they can’t defend themselves. They can’t fly yet [until they shed the exoskeleton].”

The cicadas have been seen in the southern suburbs and as far north as Elmwood Park and Edison Park, according to Spencer Campbell, the arboretum’s plant clinic manager. Within a week, he expects the “mass emergence” to begin.

“That’s basically when you can barely take a step without seeing them,” Campbell said. “There’s an excitement about it.”

To locate “early riser” cicadas before the mass emergence makes them nearly impossible to miss, people should look near trees where there’s plenty of sunlight. A list of “preferred hosts,” or wooded plants where cicadas often lay eggs, is available on the Morton Arboretum website. Parks and forest preserves are good places to start when looking for cicadas. Places where the soil may be warmer, like near pavement, offer a better chance at finding them.

So, when will the cicadas’ notorious buzzing begin? Experts expect the males’ mating call to start sometime next week. The singing has already begun downstate, where the soil is warmer and emergence begins sooner.

After the cicadas mate, the females lay their eggs in branches of certain wooded plants, potentially causing harm to younger trees. They’ll lay up to 600 eggs in the three to four weeks they’re above ground before dying, but only around 1% of those will make it to the next emergence in 17 years, Adams said.

Arboretum staff urged people to be curious about the insects and their phenomenon instead of being squeamish about the big bugs.

“They’re such large, gentle insects,” Adams said. “You can show them to children and not worry about them being stung or bitten.”

Baldacci said she is not a fan of the insect, and if the swarming gets overwhelming she may escape to her summer home in Michigan for a few weeks.

“It’s really strange but beautiful,” she said. “It’s setting off this natural phenomenon chain of events — I mean it only happens once every 17 years,” Baldacci said.