The Cabbage White Butterfly, Pieris rapae, and its larva (aka: Imported Cabbage Worm) is a pest of cabbages and other crops in the cabbage family. The Cabbage White is an invasive exotic (Native to Europe and not to North America) butterfly that was first observed in Canada in 1860. Samuel Scudder documented the spread of this butterfly across North America in his 1887 article, “The Introduction and Spread of Pieris rapae in North America”. The Cabbage White has spread to much of the world.
In his book, “The Voyage of the Beagle” Charles Darwin noted its absence in South America:
When man is the agent in introducing into a country a new species, this relation is often broken. As one instance of this, I may mention that the leaves of the cabbages and lettuces, which in England afford food to such a multitude of slugs and caterpillars, in the gardens near Rio are untouched.
This is no longer the case as this pest of cabbages has managed to hitch a ride to new lands and damage cabbages around the world.
Left: Cabbage butterflies mating Right: Cabbage worms chew holes in cabbage
Living With Insects Blog 
A related species, the large white European cabbageworm, Pieris brassicae, is on the list of high risk pests to watch for in the US.