PITTSBURGH -- Don’t be alarmed if you find purple boxes hanging from trees in the area. These boxes, resembling fly traps, are there to stop the spread of the emerald ash borer.

The beetle-like pest is native to Asia and feeds on ash trees. This process damages and eventually kills the tree. Tens of millions of ash trees have been killed since 2002

PA Department of Agriculture has imposed a quarantine in Butler, Allegheny, Beaver and Lawrence Counties to help slow the spread of emerald ash borer.

Pennsylvania's quarantine restricts the movement of ash nursery stock, green lumber and any other ash material, including logs, stumps, roots and branches, and all wood chips from the quarantined area. Due to the difficulty in distinguishing between species of hardwood firewood, all hardwood firewood-including ash, oak, maple and hickory are considered quarantined.

The state is placing 10,000 traps across 35 counties, including Western Pennsylvania. These traps are filled with sticky bait that is not harmful to humans or wildlife. These traps can be found about every 1.5 square miles.

It is part of a nationwide survey to see of the ash borer has spread. Last year, the pest shows up in Allegheny and Butler Counties. This survey will be complete in August, with results coming soon after.