To expand on Shoe's argument, I still think you should investigate on your own... Workers generate "wrecks" that are more like eggs, and they hatch after a time, with or without the help of a nearby queen I'm not sure. Workers remove planetary resources to produce these eggs, and will use the wrecks of ships they've destroyed as well.
////spoilers! You might be better off investigating.
Disappearing wrecks indicate the presence of the Star Swarm. They loooove wreckage. The workers also generate 'wreckage' of their FACs when theyre...building them, i think.