Fire ants make mounds and not holes. The mounds start out small and become larger as the colony population increases. These mounds look rather innocent until you disturb them, and ALL of the ants boil out of the mound all at once. Again, there is never a discernible hole.

I never worry about ants in my yard and garden, other than fire ants. Fire ants can be a problem for humans, pets, bird nests, beneficial insect eggs and larvae, and such.

There are some few reports of isolated nest of Fire Ants in Maryland so your best next move is to contact your local office of the University of Maryland USDA Cooperaive Extension Service and ask about them. The single best source of information about Fire Ants is Texas A & M because every one else that has any information about these buggers copied from TAMU.

Here is a link that might be useful: UMCES