This spring I've noticed a bunch of holes almost everywhere on my property which is located in Doboj, Bosnia and Herzegovina, Europe. N44.73, E18.08.
The holes are forming some kind of clusters, from 2 up to 10 holes. The diameter of the holes is about 2 - 3 cm (.75 - 1 in), and most of them are angled, not vertical. Unfortunately I forgot to check how deep they are.
What could make these holes and how should I treat them if they are made by some animal (pest)?