Spread disease because they can scavenge for food in garbage areas, dog excrement and other unsanitary areas. These disease carrying organisms can then be tracked into our homes and onto our food.
Bite and Sting: There are some species of Ants such as Fire Ants that can both bite and sting and cause much discomfort.
Have unsightly ant trails and mounds. In some instances ants have caused cracks in paths due to their excavations.
Any of these signs will likely warrant an ant inspection.