Arachnids

As the United Citizen Federation expanded its territory across the Galaxy, it came into contact with the Arachnid Species covering an area of it. The Federation initially considered the Arachnids to be a less advanced civilization. However, to avoid conflict, the region of space the Arachnids had colonized was Quarantined to prevent any humans settling within it. Despite this unofficial colonies were created, on Arachnid planets often ending in the Arachnid attacks of these poorly defended colonies leading to massacres such as at Port Joe Smith. In response to these intrusions into Arachnid colonies, the Arachnids launched an Meteor Attack on Buenos Aires. (Source: Starship Troopers wiki)