In summer yellow and red ants may appear in lawns. Both types are carnivorous ants which prey on small insects. The red ones are aggressive and can give a bite which may cause irritation and even draw blood. Being nipped by a red ant might alarm a small child, but the bites are not dangerous.
Red and yellow ants are mostly found in light soils, and in areas where they can make nests in cracks and crevices in the soil as well as in walls and paths.
Boiling water poured down the crevices will easily kill off a lot of ants without using chemicals, but to get rid of an ant colony of any type completely, you have to destroy the nest itself.
If you do manage to uncover a nest by following the routes the ants take, water it thoroughly with a spray-strength solution of the insecticide. Usually the nest is some way from the point at which the ants emerge into the open and is difficult to get to. In this case, put down insecticide dust wherever ants are busy. The worker ants will carry the poison particles back to the nest.
It will be a while before numbers are reduced. You may have to renew the bait several times over a period of weeks. In the spring, dust the area once more to catch the ants when thev come out of hibernation.