Going
Wild

Sometimes domesticated animals like cats, dogs and horses become wild or
feral. Feral animals can cause problems for native plants and animals. Some plants in Hawaii are endangered because feral pigs eat them and destroy them by rooting around for food. Feral cats can kill native birds. They are especially dangerous to ground-nesting songbirds.
Big Mistakes

Some exotic species are introduced by accident. The zebra mussel is native to the
Balkans. The Balkans are in South Central Europe. It was brought to the U.S. when ships dumped their bilge water. The bilge water contained zebra mussel larvae. The mussels grew and attached themselves to underwater parts of boats. When those boats moved from place to place the mussels colonized the new areas. Zebra mussels cause problems in many lakes and rivers by clogging up water supply pipes. They compete with native animals for
zooplankton. Zooplankton are microscopic animals that are an important food source for many organisms.
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