Margaretha blog

The mystery behind the metal dog tags on Chicago trees

Jake Malooley, Time Out Chicago

Question: I've noticed that some of the trees in my neighborhood have been "tagged." It looks like a metal dog tag but seems to be some sort of official City of Chicago thing. Does this mean the tree has been treated or has some sort of significance?Meredith Konrad, Ukrainian Village

Answer:Think of that peculiar-looking silver-dollarsize coin screwed into the bark as a guarantee your precious tree won't be destroyed by invasive species any time soon.

Specifically, the tree is protected from the evil clutches of the emerald ash borer (EAB), a tiny green beetle native to Asia discovered in the U.S. in 2002 (and Chicago in 2008) that has the power to take out an adult ash tree in two to four yearswith a little help from its friends. While the adult beetles eat the ash's foliage to little consequence, the larvae feed on the bark and inner wood, cutting off the tree's nutrient flow.

Arborjet, a Massachusetts-based tree injection technology company contracted by the city to control the pests, uses the tags to mark trunks it has pumped full of insecticide. And thank God for that poison, too, considering 20 percent of the area's trees (about 95,000) are ash. To an EAB, Chicago must look like one big Old Country Buffet.