What is the difference between an introduced and an invasive species? An introduced species is not necessarily harmful to the environment; an invasive species has a negative effect.
An introduced species is not necessarily harmful to the environment; an invasive species has a negative effect.

An introduced species is brought in on purpose; an invasive species is brought in by accident.
An introduced species is brought in on purpose; an invasive species is brought in by accident.

An introduced species is new to the ecosystem; an invasive species has been there a long time.
An introduced species is new to the ecosystem; an invasive species has been there a long time.

An introduced species is added in by humans; an invasive species enters new ecosystems on its own.