The evolution of eusociality

eusocialism-defector-egg-sneakerIf there is a gene that makes you eusocial, making you raise the offspring of other individuals, how does it spread? How can your eusocial gene end up in the next generation, if the carrier of the gene does not reproduce? And how is it possible that a gene that makes a worker produce a few offspring that is raised by the colony does not spread in an eusocial population?