Some species of Brachiaria were probably first introduced unintentionally to the Americas in the colonial period, from slave ships.

Rats and mice were unintentionally introduced while mink escaped from fur farms.

Although many new species are unintentionally introduced to new environments each year, many cannot survive outside their native habitat.

Unintentionally introduced by Spanish conquerors, smallpox ravaged Mesoamerica in the 1520s, killing more than 3 million Aztecs.

A small beetle unintentionally introduced from the Mediterranean region feeds on Malta starthistle seed heads, but has had little effect in controlling the plant.

A species that occurs naturally in an area, and has not been introduced by humans either intentionally or unintentionally Allaby 2005).

"Others were introduced unintentionally."

Cheatgrass, an invasive species which was unintentionally introduced, forms a critical portion of their diets.

It is likely that this aquatic plant was introduced unintentionally in the early 1960s.

In New Zealand, the Pacific oyster was unintentionally introduced in 1950s, most likely through ballast water and from the hulls of ships.