Starseeds, also called Sailseeds, are large (thousands of meters, or approximately 1 mile in diameter) nonsentient species that travel through interstellar space. A starseed is typically spherical, but when it needs to change direction it unfolds itself into a large squarish solar photon sail with the four corners connected via strands to a small knob. Most of the internal organs are located in a cross-shaped swelling in the sail. Nothing is really known about them, other than they seem to migrate from the galactic center to the rim of the Galaxy to eject their eggs, and then the chicks begin to travel back to the Galactic Core, a journey of 50000 LY. Sometimes the eggs are ejected towards other galaxies, but most are left to hatch and migrate themselves to the core.
Starseeds are in fact packages of microorganisms designed to seed new planets with life, thus creating new customers for the Outsiders. They are reluctant to reveal this information because they are ashamed, since one of their starseeds created the Thrintun, which destroyed nearly all intelligent life in the galaxy several billion years ago.