According to a new study published in the journal Nature Ecology and Evolution, the first louse to take up residence on a mammalian host likely started out as a parasite of birds. That host-jumping event tens of millions of years ago began the long association between mammals and lice, setting the stage for their coevolution and offering more opportunities for the lice to spread to other mammals.

The study was led by Illinois Natural History Survey ornithologist Kevin P. Johnson and Jorge Doña, a Marie Curie postdoctoral researcher at the University of Illinois Urbana-Champaign and the University of Granada, Spain.