The IGRs take longer to work but their effects last longer. Contact insecticides work by killing the ants touched. To kill an entire colony, a contact insecticide must come in contact with every ant. When improperly used, these are the products that often cause people to notice that the ants just seem to move after application. This can happen especially when granular products are not watered in after application.
Contact insecticides come in all forms, including mound drenches, dusts, granules and aerosols.
Be sure to read and follow directions closely before applying any insecticide.