Garden ants are harmless and are not a public health pest.
During summer, winged females and males leave the nest on one or two warm days and take flight. During this flight the ants mate and they sometimes fly inside buildings. Ants usually go in to houses for food which is sweet and sugary. Once one ant finds food, there will soon be others and a trail of ants taking the food back to the nest.
We recommend that householders should treat for garden ants themselves. If possible, trace the trail of ants to the nest - you can normally see the opening by small piles of fine earth surrounding the entrance. You can treat by pouring boiling water into the nest or use an insecticidal dust or spray for controlling crawling insects outside. Please make sure you follow the instructions on the label carefully.
There are local and national companies that can also provide a similar service, try searching a local telephone book or the Internet for pest control.