So they are a bio-weapon developed by "civilised" species. Seems like a complete failure given they seem to be impossible to control. Though perhaps the species that developed them have a mind control device that lets them direct the aliens and stops them from just running amok.
Alternatively they are a genocide tool, just drop the pods onto a planet who's people you don't like and the aliens will wipe them out. If you have an alien-specific virus that will kill all the aliens then you can kill them off once the planet has been cleared of unwanted inhabitants and then you can move in and take over.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix
