Aphids

5768  The attached photo was taken in the Boundary Waters of Minnesota in August, on the bark of a birch tree. It appears to be a tight cluster of fifty or sixty black 1/4″ six-legged insects(?), being “herded” (so it appears) by six or eight large black ants moving around the perimeter of the cluster. (You can see a couple of the ants on the periphery if you look carefully.)  Any help? Thank you.  Dick

These are aphids (Hemiptera/Sternorrhyncha: Aphididae), also known as plant lice, being tended by ants. The ants provide the aphids some protection against predators and in turn feed off the sugary secretions (‘honeydew’) of the aphids. Ed Saugstad, retired entomologist; Sinks Grove, WV.