I agree, moles hills seem the most likely but how small do you mean by the word 'small' ?
Potter bee's for an example leave small volcanoe shaped heaps of excavated earth approx an inch (2.5cm) across, complete with the hole in the middle.
There are very many of them in different areas ranging in sizes. The sizes can be from four centimetres to 15 centemetres in circumference. They look dried out. They are brown, like the colour of feces. At first I thought that's what if might be except each mound has a hollow in the middle. They kind of remind me of clay pottery that has been spun on a wheel, except there are lumps and bumps around the outside. Some other thoughts might be insect nests.
Thank you for all your answers. I talked to a neighbour today and he said they are made by frogs, which makes sense, since we live near a marsh. The frogs burrow into the ground in the fall. When they are ready in the spring, they come out of their burrows and the end result are these dried up mounds.
This is a very good example of why the country of origin should be next to the poster's name, especially in this section. Moles or bees definitely.......but never frogs.
Unless stated we imagine all Q's come from the UK, but now see that annalouise must come from the USA (I hope!).