Aliens

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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They infest our lakes and rivers, disrupt our skies, ravage our forests, and devour our gardens. Sometimes these non-native plants and animals arrive through human carelessness, sometimes by human design, but without natural predators, many spread rapidly to wreak havoc on the local ecosystem.

Nationally, close to half the 958 plants and animals listed as threatened or endangered are at risk primarily because of these unwelcome invaders, which every year cause an estimated $138 billion in damage.

Several recent frightful incursions here—by the Asian long-horned beetle, the silver carp, and the emerald ash borer—prompted us to seek dossiers from the Field Museum, which houses one of the world’s largest collections of biological and anthropological specimens.  Here are some of the most notorious.


NAME: Silver carp (Hypophthalmichthys molitrix)
ORIGIN: Eurasia
DATE INTRODUCED: 1973
HOW IT GOT HERE: Imported to control algae in aquaculture ponds; escaped into the Mississippi River in the early 1990s

“Right now, the silver carp is probably the number-one threat [to the aquatic ecosystem], in terms of invasive species,” says Philip Willink, a fish biologist at the Field Museum. Originally brought here by catfish farmers to rid their ponds of algae, the fish escaped into the Mississippi River basin after storms flooded the ponds. Though silver carp—and their close relative, the bighead—haven’t yet spread to the Great Lakes, they have been making their way up the Illinois River and are now within 50 miles of Lake Michigan, contained only by an electrical barrier built by the Army Corps of Engineers on the Chicago Sanitary and Ship Canal. Along the way, these large, ugly filter-feeders have been devouring plankton—a vital source of food for larval native fishes. “They’re basically wiping out the bottom of the food chain,” says Willink. They’re also nuisances to boaters because they often jump out of the water at the sound of boat motors, occasionally injuring the people on board.

THE FIGHT: So far, the electrical barrier has kept silver carp from infesting Lake Michigan, but scientists worry that these feisty and resilient monsters could get through.

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