Seeing large black ants and flying ants in the spring and summer months isn't unusual. This is the time when colonies are growing, hunting for food and water, and generally establishing themselves. Flying ants are often young ants that will later lose their wings, however what you're seeing could also be termites. It's important to figure out which problem you have in order to get the best product for treating your home.
The most common large black ant problem in a home is caused by carpenter ants. These insects get their name by their preferred living space--namely damp, rotting wood. While carpenter ants do not eat the wood, they do bore into it to make space for their colony. This behavior is very destructive to the wood in your walls, and makes finding the ant colony vital as soon as there are signs of infestation. Specifically watch for small piles of sawdust on the floor inside or outside the home. Sometimes termites might be mistaken for large black (or carpenter) ants. To know which is which note that carpenter ants have narrower waists and bent antennae compared to termites. Also termites tend to be stealthier. They don't like to come out into the light whereas carpenter ants will march brazenly through your home, very often during the night looking for sources of sugar and protein.
Winged ants are reproductive insects often born immediately after a period of heavy rain. You may see them moving in a swarm as part of their mating ritual. When they appear, all mating takes place in one day after which the females begin seeking a spot to establish a colony. The males die. While the visual impact of swarming might be disconcerting there's nothing to worry about. The ants are leaving the colony, not returning to it. The only time for concern is when you see winged ants coming into the home. This can indicate that you've got an established colony of carpenter ants or pharaoh ants somewhere in your walls. As with large black ants you want to be certain that what you're seeing is, indeed, an ant. Termites have long bodies that are not separated into three distinct parts like an ant's body.
Large black ants often live in the base of trees or wood piles. They also seek out damp wood that's been damaged by cracks in a house's siding or because of poor drainage. They may also look to piles of paper or insulation as a nesting spot. Winged male ants only live for the day of mating, so it's not as common to find them inside the home (if you do see a lot of them, that's a sure sign of an interior nest). If you feel you may have a primary or satellite ant colony somewhere in your walls, it's important to locate it as soon as possible for remediation. It will simply keep growing otherwise, causing ongoing damage to wood structures.
The best way to prevent large black ants and flying ants from infesting your home is by making sure your home stays dry. Clean out your gutters, check downspouts for proper drainage, keep trees and hedges well trimmed, and move any wood piles away from the walls of your home. Also look around your house for any obvious cracks or openings that a queen could use for access in trying to set up a nest.
Once you know you have an ant problem the next step is remediation. First, you need to find the nest. You can often track ants back to their colony if you watch for them at night (particularly in spring). If the ant goes outside, you can breath a sigh of relief as you won't have to tear up walls. However, still locate the colony and clean it out before they try to set up a satellite nest inside the home. The key difference between the main colony and a satellite colony is that the latter will be dry. When you find the nest you can then treat it with boric acid or another insecticide of your choosing. Some people simply vacuum out the ants (but you need to do this several times to be sure they're gone. If you cannot locate the nest, or find that your remedial efforts fail, get professional assistance. Ants in your walls can do hundreds and sometimes thousands of dollars worth of damage that only gets worse the longer you wait.