This is the hardy groundcover, Pachysandra terminalis (Japanese Spurge), which I planted several years ago in the back yard, to cover a dip in the ground left after a cottonwood tree was removed by the former house owner. Now this creeping vine has spread in a thick cover where chipmunks hide.
Unfortunately, now it harbors mice or small rats which I saw darting out to feed on the birdseed that have fallen to the ground. This weekend we'll mow half of the pachysandra down and confine it to the dip in the ground. It had moved over into the grass, and though it looks lovely, it's gone wild, in more sense than one!
I may even stop feeding the birds for a while to make sure the rodents clear out. Where is that roving black neighborhood cat, the one that used to patrol the backyard in the mornings, now that I need it?