What's the worst sin of globalization? To hear some tell it, it's not unfair wages or job losses, but those little tagalong critters known as invasive species. World trade has enabled flora and fauna to set up camp far from home. Consider: European hedgehogs have arrived in New Zealand, and zebra mussels from the Caspian Sea have shown up in the Caribbean. Many scientists contend that alien species wreak havoc on native ecosystemsé, crowding out indigenous life-forms. But another word for invasion is migration, a natural process that dates back to the moment the first clump of cells crawled out of the primordial ocean. Today, some evolutionary biologists say that the invasive-species hysteria is just pseudoscientific xenophobia and that these so-called incursions are natural selection in action. After all, the human race is one of the worst invasive species out there. Darwin would be proud. - Patrick Di Justo
Mesquite
This tree competes with native species for water.
Type: Land
From: US
To: South Africa, Saudi Arabia, Puerto Rico, Pakistan, India
Louisiana Crayfish
Adapts easily to new climates and colonizes them quickly.
Type: Aquatic
From: US
To: Ecuador, Asia, Europe, Kenya
Water Hyacinth
Considered one of the most aggressive aquatic weeds in the world.
Type: Aquatic
From: South America
To: US, Guam, Australia, Papua New Guinea, Japan, China, Fiji
Nutria
The burrows of this giant rodent damage riverbanks and dikes.
Type: Land
From: South America
To: US, Europe, Kenya, Asia
African Tulip Tree
Crowds out crops and other trees as it grows, becoming predominant.
Type: Land
From: West Africa
To: Samoa, Cook Islands, Hawaii, Guam, Fiji, Vanuatu
Hedgehog
A threat to native invertebrates, reptiles, amphibians, and birds.
Type: Land
From: Europe
To: New Zealand
Common Tilapia
Has spread worldwide thanks to aquaculture. Farmed fish: It's what's for dinner.
Type: Aquatic
From: Southern Africa
To: US, Brazil, Honduras, India, Australia, Algeria, Egypt
Zebra Mussel
Has traveled around the world in ship ballast water.
Type: Aquatic
From: The Black Sea
To: Europe, Canada, US, Jamaica, British Isles
Black Spotted Goby
Preys on young fish, fish eggs, aquatic insects, and small invertebrates.
Type: Aquatic
From: The Caspian Sea
To: Canada
Kahili Ginger
Spread by birds and garden waste; a major problem in New Zealand.
Type: Land
From: India
To: Hawaii, Cook Islands, South Africa, New Zealand, Micronesia
Purple Loosestrife
Invades wetland habitats and crowds out food sources for birds.
Type: Land
From: Europe
To: Australia, Ethiopia, US
Goat
This voracious eater is particularly destructive to island ecosystems.
Type: Land
From: Central Asia
To: Fiji, New Zealand, Puerto Rico
Wakame Seaweed
Its growth poses a problem for marine farms. Would you like miso soup with that?
Type: Aquatic
From: Japan
To: Australia, Tasmania, North Atlantic, New Zealand
Mudsnail
Has been known to take over rivers; can hitch a ride on hikers' boots.
Type: Aquatic
From: Tasmania
To: Australia, Europe, US
START
The Best: 10 North American Geek Fests
The Alien Invasion
