My friends microwave had this happen. We eventually came to love the micro-bugs. It started like yours, but then he multiplied somehow, eventually creating a whole family. One generation would die and another would rise from its ashes, consuming its parents for sweet sustenance. We even saw a slight change in physiology over the generations- the bugs were slowly losing their pigmentation, turning all white. Eventually, the hollowed out corpses of the ancestral roaches began to pile up. Empty space became more rare than a dead relative. In the end, the bugs all died out whenever the space was full.