So, after watching the first season of FS, I realized that it takes a lot of ideas from the 1957 argentine comic "El Eternauta":
1) Skitters: The common enemy in the series, they have an harness in their backs, so you can assume they are controlled by another alien.
Cascarudos (bugs): The basic infantry in the comic, they have a "radio" attached in their nape, controlled by another alien.
2) The childen: The Skitters (and mechs) kidnaps the children and they get implanted with the metallic obideance device, wich controlls them. They use them as slaves and sometimes like soldiers, being capable of talking.
Robot-men: The cascarudos donīt kill all of the survivors, some are kidnapped and implanted with a radio device in their napes, just like the bugs. They can talk and are used as basic infantry against the remaining army.
3) Humanoids: They look like the bosses of the Skitters. Humanoids and capable of flying ships.
Manos (hands): They control the cascarudos, robots and gurbos (another alien) with a console, using their multiple-fingered hands. They are slaves too.
Also, there are anothers details, just like the weapons (they kept the most powerfull ones for the end). Letīs see the next season...