The ash borer beetle has killed millions of trees around the country, and it's spreading like wildfire. Some counties even have to be "quarantined" if the beetle shows up.

The ash borer was first seen in the U.S in 2002 around Michigan, it most likely caught a ride to American on firewood transported from Asia,, reported.

The beetles leave telltale "D" shaped entry holes in the trees they infest, which usually die between two and four years of the initial assault, the N.Y. State Department of Environmental Conservation reported.

The parasites are responsible for the death of over 50 million trees in the U.S. since their initial introduction.

The beetle has now spread to "Connecticut, Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland, Massachusetts, Michigan, Minnesota, Missouri, New Hampshire, New York, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and Wisconsin" and even more states are in danger, reported.

The beetles usually don't fly more than half a mile away; they are mostly spread by humans moving infested firewood to a beetle-free area.

The beetle showed up in Iowa for the first time in 2010 and has spread across the state, now certain counties are being quarantined, which means a permit will be required to move firewood out of the area, The Christian Science Monitor reported via the Associated Press.

State officials are still working on the logistics of the quarantine.

"We hope in future weeks we will have that quarantine worked out, we will have worked with industry to fully inform everyone and hopefully draw up a good quarantine plan," state entomologist Robin Prusiner said.

Since the trees take a few years to show signs of devestation, it is still unclear how much damage has already been done.

The state has about 52 million rural ash trees, the main target of the ravenous beetle. There are also about three million other ash trees located in urban areas.