Ants use pheromones to create trails that lead to sources of food. The interesting part is that the pheromone trail that they create can only last for about 3 days. Therefore, any time there is a sharp decline in outdoor temperature, ants begin to retreat to their den in order to escape the colder temperatures. When colder temperatures persists for more than three days, the pheromone trail fades.
So when the weather warms up and the ants return to the surface, they move into a random forging phase. This is when they begin to infiltrate your homes and yards. So now that the weather is starting to warm, you must be proactive against ants before they wander into your yard or home.