Exotic animals and plants are crisscrossing the globe as never before. Many of these unwelcome species have found their way to the Chicago area and are wreaking havoc on our local ecosystem.

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NAME: Common teasel (Dipsacus sylvestris)
ORIGIN: Europe
HOW IT GOT HERE: through contaminated seeds

These stalky, prickly stemmed biennial weeds, which can grow eight to ten feet tall when flowering, have spread rapidly over the past 20 to 30 years, largely in areas disturbed by development. “Teasels pretty much come in where there’s opportunity,” says Laurel Ross, an urban conservationist at the Field Museum. “Highways and roadways are an opportunity—they’re big open areas with lots of sun.” Because its lilac or white flowers develop into large oval seed cases whose spines were used for teasing cloth, the plant is also known as a gypsy comb. A single teasel plant produces thousands of seeds, most of which will germinate.

THE FIGHT: Applying herbicide to the rosette kills the plant’s roots and prevents it from resprouting. Flowering stalks may be cut down, but seeds often continue to develop and mature even after cutting. Remove the cut stalks to prevent the seeds from dispersing.