"Invader" is another term used for the Martians in the War Of The Worlds story. In Stephen Spielberg's 2005 cinematic rendition of the classic alien invasion, the creatures that attack Earth are never referred to as "Martians" or specified as coming from Mars at all. According to Spielberg's commentary on the War Of The Worlds DVD, these invaders do not come from Mars but from some other dark corner of the universe.
Whereas H.G. Wells' impression of the Martians resembled giant octopi, Spielberg's invaders look like nothing ever seen on Earth. Their bodies are strangely angular and topped by a large, wedge-shaped head with dark reflective eyes, a fanged mouth and no nose. A crevice beside each eye may serve as the invaders' means of hearing. The creatures walk on three long, multi-jointed legs which end in three-digit feet. Each digit ends with a sucker-like tip that lets them grip objects. The invaders' feet are very flexible and can manipulate and grip objects like hands. They also have a pair of arms, but the arms are short and appear to be rather feeble.
The invaders only appear on screen during two scenes in the film, the rest of the time they spend inside their Tripod fighting machines. The Tripods appear to have been constructed in the likeness of the invaders themselves.
War of the Worlds (2005)
Unlike the book, Spielberg's invasion takes place in the 21st century and starts out quite differently. The invaders had apparently buried their war machines on Earth an unknown length of time before the film's events, though it is speculated that they may have done this before humanity even evolved to its present state. When the invasion commenced, they encased themselves in some form of capsules that "rode" on bolts of lightning straight into the ground and into the Tripods' cockpits. The cascade of lighting that occurs as the invaders arrive creates an electromagnetic pulse that disables virtually all electronic machinery in the areas they happen, so when the Tripods arise from beneath the earth, the humans are unable to fight back or even flee fast enough to escape the alien onslaught.
For several days, the invaders slaughter a large percentage of Earth's population. Anyone who isn't killed immediately is captured and taken aboard the Tripods where the invaders feed on their blood or use it as fertilizer to seed the land with red weed. Even when the military manages to mount a counter-attack, Earth weaponry proves to be utterly useless against the Tripods' shields.
Just like in H.G. Wells' original story, the invasion is doomed from the start as the aliens have no immune systems to protect them from the countless forms of bacteria found on Earth, and so the invaders all die as they are exposed to even simple diseases that humans are able to tolerate.