This is an unnamed spacefaring alien species which briefly invaded Earth.
They are very athletic, being able to jump up to the roof of a farmhouse that is about ten feet off the ground. Their skin changes colors, giving them a camouflage ability- which is how they remain unseen throughout most of the invasion. They also have a spike that protrudes from their wrists that expels poisonous gas. Water is their weakness, as contact with it seems to "burn" the alien and cause it great amounts of pain.
This species has clearly established their ability to master space travel in order to get to Earth. Their ships can primarily be seen at night via the yellow-orange lights that show that they are in fact saucer shaped craft. Graham Hess asked his brother Merrill if there had been any new development, and Merrill explained that a bird hit something in the sky and fell straight down; explaining that they did in fact master cloaking technology. It is also unknown what kind of weapons these creatures possess due to the fact that they did not use them.
Despite their advantages over human technology; there are several pieces of Earth technology that they are, frustratingly, not familiar with, such as doors; which they seem to have trouble getting through, for some strange reason. They also have trouble getting through wood as well, again, for whatever reason.
- Although the reason for the alien's attack has never been officially stated, a survivor heard on the radio in the basement states that they came to harvest humans. He backs this up by stating that he and his friend saw the aliens poison his friend's family and drag away the bodies. This is extremely unusual, because the alien's weakness is water and 50-65% of human bodies are water. Now obviously they must not have known this beforehand. However, thanks to the family mentioned above, they must have definitely found out through them and then, realizing they messed up and are invading a planet whose surface and inhabitants are filled with the very substance that can kill them, promptly retreat and leave Earth.
- Due to liquid water acting as a very corrosive form of acid to this species, it is possible that their homeworld's natural bodies of liquid are a substance other than water, and water may be completely alien to them. It is possible that they only found out about water being their weakness when they attempted to invade Earth. This weakness is likely due to their body chemistry being radically different from humans, but still able to survive in Earth's atmosphere.
- As shown, they obviously have the technology to navigate between planets, but it's unknown if they have any type of advanced weaponry or not. This is explained in the movie through a book which theorizes how an alien invasion would occur, and according to the book, if the aliens used their technology to attack, humans would retaliate with nuclear weapons, rendering the planet's resources useless.
- For some reason, despite having achieved intergalactic travel capabilities, the aliens wear no clothes. This may be due to their need to exploit their skin's natural abilities of changing color like a stealth suit. While from our perspective it may seem odd that a space-faring species would not wear any type of clothing, it should be noted that clothes are a human concept and are usually dictated by culture. Since this is an alien species, they can't be expected to mirror every aspect about us regardless of how intelligent or technologically advanced they are.