Pre-industrial Tuchanka was a world teeming with life, much of it large and predatory. The krogan were the only sapient species on the planet, but even with their superior intelligence, only one newborn krogan in a thousand could expect to survive to maturity amid the hungry megafauna of Tuchanka.
Being very tough humanoids with an extremely high reproductive rate, the krogan managed to survive in this harsh environment long enough to develop advanced weapon technology. Superior weaponry reduced the threat of Tuchanka's native predators, but the krogan soon found themselves competing with each other for resources. This competition ended in a nuclear war that devastated Tuchanka's environment.
A few of Tuchanka's native species have escaped the planet to become threats on many other worlds, including the following: