The ants will not destroy your plants but they could be living in wood used to build your raised bed. If you find a nest you can try pouring boiling water into the crevice where the ants live. Ants can also place aphid on plants to milk them for honeydew later. There are many sizes and types of ants. Carpenter ants are larger and burrow into rotting and damp wood. Tiny sugar ants like to enter homes. Some ants bite or sting. Some do little or no damage. A bit more research can tell you what type of ants are on your plants. Keep growing, Marianne Binetti