The Illinois Department of Agriculture wants residents to pay attention to where they're getting their firewood.

State agriculture experts say knowing where firewood originated can slow the spread of the emerald ash borer. The pest is responsible for the deaths of millions of ash trees. Illinois Department of Agriculture spokesman Jeff Squibb says the preference is to purchase and consume firewood locally.

Experts say they think infested firewood that has been moved across the state has helped spread the ash borer.

Emerald ash borers are about a half-inch long and a metallic-green color. They were first found in Illinois in 2006. About 40% of the state is under quarantine, from Chicago to Marion County.