They are the result of ants pushing out sand from underneath pavers for nesting purposes. When this starts to happen, it can cause the pavers to become uneven and/or drop. This completely ruins the look of your paved outdoor areas and is a trip hazard just waiting for an accident to happen.
Before you head off to the hardware store for something to get rid of them, you should know that ants are one of the most difficult insects to control. At any one time, what we see on the surface is only a tiny proportion of a colony, so store-bought solutions will only be successful for the short term, if at all. Most of the colony will remain safely underground and will simply relocate to another area of your garden or resurface a few weeks later.
Your ant problem is best left to the experts, so give your local pest control professional a call. They have the skills and experience to identify the type of ant, apply the most effective treatment and save your paving.