They definitely secrete some sort of chemical or biological compound to do this. They're capable of it since that's how they build their hives.Not going off of any canon but the first movie, my thinking would be once they ate enough they would grow larger and start spitting out eggs.
No mention of any retroviruses though IIRC, but since they retroactively introduced the whole Black Goo thing (like instead of planting an embryo which uses half of the host's genetic material to finish itself as in the "old" canon, the glob of Goo uses the host's own cells and material to create the embryo from scratch), it might have something to do with Egg Morphing.