Recently I've been creating a race of parasitic Aliens that eat entire Solar systems. So basically, the alien queen arrive's on a planet or moon that exists inside of a solar system. Then the queen burrows into the planets surface by eating through. She then creates her nest underground and begins to give birth to the workers and soldiers. The workers begin to dig a system of tunnels while the Soldiers scout the surface for life. The queen will then burrow down to the planets core and begin to carve out a cavern for its eggs. It will proceed to lay three eggs, then it will die. The soldiers and workers will also die. After less than a year, the three eggs will hatch queens. They will then eat the body of their mother and the rest off the planet. After this happens they will then spread out towards the rest of the planets and moons in the solar system.
The aliens are completely Organic, and primitive. The only things they know are eat and kill.
How would they get to these other planets?