These do look like ants and ant hills, but we can't determine what species they are from the photos. (There are over 100 ant species documented in MD.) They can be left alone since ants in the landscape are beneficial in many ways, helping to aerate the soil and preying on a variety of insects that gardeners would consider a pest or nuisance. They do not harm plants, and knocking down anthills would not affect the colony much or for very long since they will just rebuild the mound afterwards since it is the entrance to their underground nest.

Miri