Experts say the “tick explosion” predicted for the area on social media will not happen, but the freckle-sized terrorists are here to stay.

State Department of Health data on cases of Lyme disease show that of the 11,443 cases in 2016, Butler County had the most at 641 cases.

The next-highest number of cases in the counties surrounding Butler was Allegheny County with 403 cases. Butler County had the fifth most cases in 2015 and the second most in 2014, the state data shows.

Lauren Robinson, the health department's deputy secretary for health promotion and disease prevention, said one benefit of the high number of Lyme disease cases in Western Pennsylvania is the attraction of more resources to study ticks and the diseases they carry.

She said increased awareness, diagnosis and treatment of Lyme among county doctors may also account for the elevated numbers.

Michael Skvarla, director of the insect identification laboratory at Pennsylvania State University, said the prevalence and proximity of the ticks' host animal, and not any weather or climate issues, determine the tick population in Western Pennsylvania.

He said the most common tick in the area is the black-legged tick, which carries Lyme disease and transmits it to humans.

At the larva and nymph stage, baby and juvenile ticks feed on the white-footed mouse and on deer and other large mammals as adults.

“That's why they get on people,” Skvarla said. “We fit that large mammal type.”

He said the ticks embed in the skin and feed on blood, but in doing so can transmit Lyme disease if an adult tick's host is a human.

Expansion of homes into former farms, fields and woods, Skvarla said, has displaced mice and deer and even invited them closer to humans through landscaping.

That means humans are in closer proximity to ticks' host animals, and therefore to ticks themselves. The situation, he said, is likely a major reason for the increased cases of Lyme disease in Western Pennsylvania.

“It's mostly because we are modifying the rural areas,” Skvarla said.

He said while mosquitoes have preferences according to blood type, ticks are opportunists who just want to land on a warm mammal.

They can sense the vibrations of an approaching person or mammal and have receptors that pick up on the presence of the carbon dioxide mammals exhale.

Skvarla said ticks are also known for “questing,” or hanging off a leaf or blade of tall grass with their front legs in the air so they can easily hop onto a host for a meal.

Penn State scientists are not working on projects to rid the state of ticks because they are native. The sheer number of ticks precludes a large-scale spraying project, and there are no parasites that can be released to destroy them.

He said the best way to avoid Lyme disease — which can cause a myriad of symptoms including flu-like symptoms, joint or generalized pain, fatigue and cognitive decline — is avoiding ticks.

Ways to do so include:

Spraying the shoes, clothing and skin with an insect repellent containing 20 percent DEET

Checking the entire body for ticks immediately after being outdoors

Removing brush piles or thick growth where mice and deer might congregate

Treating lawns with a tick spray that is not harmful to pets or humans

Those who find a small tick embedded in their skin or scalp should remove the tick with tweezers and kill it.

Ticks that are engorged should be removed by a doctor, Skvarla said.

In addition to black-legged ticks, which are the size of a freckle, American dog ticks can spread Rocky Mountain spotted fever.

While the incidence of that disease is low in Pennsylvania, it can be deadly if left untreated.

Lone Star ticks, which are now found east of the Appalachian Mountains, also carry Rocky Mountain spotted fever, Skvarla said.

Robinson said common misconceptions regarding ticks are that fishermen or swimmers are not at risk because ticks cannot live in a wet environment, and that a hard winter kills off ticks.

“They're pretty hardy creatures,” Robinson said.

Research on long-term, chronic Lyme disease is ongoing, Robinson said, but diagnosis is difficult because victims present a wide variety of symptoms to doctors.

“More research is needed,” she said.

Skvarla delivered the bad news that all Western Pennsylvanians dread: ticks are here to stay and diligence is the only reliable way to prevent Lyme disease.

“It's just kind of the way it is now,” he said.