From you picture it is difficult to see what you are talking about.

If these are little holes surround by mud, then it could be common earth worms.

In looking at the pattern of the "holes" they could be the foot prints of some animal that passed through the area. The look somewhat like cat foot prints.

To answer you question more information is needed, ie picture take closer to the hole possibly from a side angle to get a better idea of what is around the hole.