The Scarab was a class of droid starfighter used by the Trade Federation during their attack on Naboo. They were slower (in movement, maneuvering and attacking) than the infamous and more commonly used Vulture Droid Starfighter, but they were tougher, possessed shields and could operate independently, without relying on the Droid Control Program.
The Scarabs were used extensively in the Outer Rim worlds to subjugate worlds that opposed the Trade Federation. Their manufacturing facilities were hidden away on the remote volcanic world of Eos, which were discovered by mercenary Vana Sage by following a damaged Hunter-Seeker Droid. Vana had earlier participated in the testing of the Scarab Droids, shooting down several waves of the prototype fighters deployed from a Federation Landing Craft. After intercepting a transmission regarding a failed attack on the Queen's Starship, Vana was betrayed by her employers, who sent Hunter-Seeker Droids and hired guns to kill her before she could expose their dirty secret.
After the incident over Eos, they were used en masse in various Outer Rim conflicts, as well as the invasion of Naboo. At the world of Lok, mass amounts of Scarabs supported Trade Federation armor in the fight against the pirate group known as the Lok Revenants. During the assault on the pirates' base, Scarabs filled the sky, providing air support for the huge army of AATs that stormed the fortress.
Though their main manufacturing facilities on Eos were destroyed by the leader of the Lok Revenants, the Feeorin pirate Nym, the Scarab was still used by the Trade Federation up to the Battle of Geonosis.