Skitter

The Skitters are an extraterrestrial species which invades Earth and nearly drive the human race extinct in the TV series Falling Skies.

These are hexapod creatures with a reptilianoid-insectoid appearance. Their six legs are arranged in radial fashion but their upper body is quasi-humanoid, containing a pair of arms and a head, giving them a body plan somewhat similar to the Tholians from Star Trek. Each hands and feet have three digits.

Skitters are nocturnal and appear to be a very hostile species, as no clear reason has yet been given for their brutal assault on Earth. Their technology includes large robotic soldiers which, unlike the Skitters, are oddly bipedal. Furthermore, the way Skitters give verbal orders to the robots have led some to suggest that the robots are actually a species of their own, which have been enslaved; or simply work for; the Skitters.

Skitters appear to have an exoskeleton, though it isn't tough enough to protect them from simple firearms. They are also known to kidnap humans and infect them with a parasitic life-form which allows the Skitters to control them and use them to communicate with humans.

It turns out that the Skitters used to be other lifeforms that were transformed into Skitters by the harness technology, which is controlled by the Overlords.

They also have two strange clawed mouths.

Relationship
The Skitters are able to communicate with each other throughout cries and growls unknown to humanity. However, they appear to be slaves to the harness process, which the Overlords have inflicted to them. Because they are slaves to the Overlords, it is believed that their attacks on humanity may be against their will.

Humans: The Skitter Resistance has had quite a bit of interaction between humanity. The Rebellion and the human survivors have made a truce.

Mechs: Skitters appear to have more dominion than they do, as they give them various commands and they obey without question.

Overlords: There is a Resistance movement of skitters, vowing to overthrow the Overlords. The Overlords are extremly fearful about the Resistance and they continually hate each other. Unlike humanity, they view the Resistance as more of a threat.

Weakness
Initially it was believed the aliens had no known weakness due to there superior strength and reflexes that could overwhelm a human in combat. The resistance however discovered they do posses several weakness' thanks to chance and observation.

Prior to joining the Resistance, John Pope, an ex-con, discovered that the aliens are similar to Earth Spiders in the sense that removing enough limbs render them helpless to further attack. It was also discovered by accident with the captured Skitter that the creatures posses a nerve cluster at the back of the mouth where humans would normally posses a pallet and bone. Pressing on this nerve knocks the alien out. Also since this nerve connects directly to the brain it was discovered stabbing through it will kill the alien.