The Immortal Jellyfish

Another reason the immortal jellyfish's spread around the globe may have gone unnoticed for so long is that they don't have a perceivable negative impact. Invasive species can be problematic, and some, such as zebra mussels in North America, wreak havoc that costs enormous sums of money to fix. Others, like the hippos introduced to Colombia about 30 years ago, pose threats to the native wildlife they coexist with.