These Aliens are aquatic creatures able to control humans. They left their home world after it started to die and search for a new planet which they could take control.
This alien species lived on a planet composed entirely of oceans. For unknown reasons, their planet started to die, so they decided to go to Earth and to take control of it to survive.
They arrived in a small town in Ohio called Herrington and infected the professors of the local High School, then the students and later everyone in the town.
However, a group of students not infected managed to kill the Queen of the aliens with a diuretic drug, which killed all the aliens simultaneously.
The Aliens are very similar to fishes or tadpoles in appearance, but they also possess tentacles. Though they are aquatic, they can live out of water if they hydrate regularly. Much like insects, they have a Queen and are connected telepathically to her, meaning that if she dies, all the other Aliens die too.
The Queen is much bigger than the other Aliens, and her appearance is a lot more monstrous. She is also much more strong and powerful.
Their most notable ability is to control humans by entering into their ears. When they control humans, they apparently conserve their memories but completely alter their respective personalities (for example, a shy and inhibited person become more outgoing and outspoken, and a brash and domineering person become more understanding and compassionate).
They are also able to duplicate themselves, and they possess limited shape-shifting abilities.
In addition, they are practically immortals since they can survive even if they are cut into pieces. Even in human hosts they possess impressive regenerative powers, they are able to re-attach the host's limbs if they are cut off and can also survive to bullets and decapitations.
Naturally, they are excellent swimmers.
The Queens possess greater shape-shifting abilities, they can even change their size and turn into human. They are also able to give birth to many aliens simultaneously by spitting out larvae, and they have colossal strength.
These Aliens can't survive without water, therefore they constantly need to hydrate when they are in human bodies. If their host is too old or ill, he or she eventually dies from dehydration. But their more notable weaknesses are the diuretic drugs, which are lethal for them.