Carpenter ant signs include leaving a sawdust or frass which is essentially a by product of all their chewing. As explained in our CARPENTER ANT CONTROL article, they do a good job of chewing through wood but don't in fact eat any of it. Based on your description, it sounds like you have them in this fence and probably at this joint too.

I suggest you get some DRIONE DUST and CYPERMETHRIN. Fill one of our HAND DUSTERS with the Drione and have it alongside you when you take the fence apart so it's ready to use. I'm pretty sure you'll uncover a nest and the Drione will be ideal to use for the treatment. Once you complete the work at that joint, I suggest you dust each of all the other joints you have to insure there aren't any other satellite nests on the fence. The Drione will do a much better job than a liquid spray treatment.

Once the fence has been treated, finish the work by doing a foundation spraying using the Cypermethrin. This will insure straggler ants won't find their way into your home.

You're describing carpenter ants and I'm pretty sure the ones with wings are what we refer to as carpenter ant swarmers. These are special ants also known as reproductives which colonies send out every spring and fall to start new colonies. Since they will only emerge from established nests, it's reasonable to assume you had an active nest last year which is now releasing these ants to go and start new colonies somewhere else. Because the nest is on the home, some are finding their way inside instead of outside where they really want to be. Since carpenter ants can cause a lot of damage to wood, you'll need to treat the nest as described in our CARPENTER ANT CONTROL ARTICLE.

Since you're finding them close to the window, one would naturally think the nest is somewhere in the vicinity. In fact this is a common location for carpenter ant nests to exist. But to be sure you need to follow the directions we outline in our article on how to track ant trails and locate where they live. As you'll learn, most any carpenter ant problem will involve multiple nests and if you wish to get rid of them you'll need to get all satellite nests. Hopefully you'll be able to locate the nests and if you can, treating them with DRIONE will provide the quickest control. If you're not able to locate nests and are at a loss for where they are living but see active worker ants, a thorough TERMIDOR application could resolve the problem. If all else fails, call a service company to do the treatment. Carpenter ants can cause a lot of damage and any activity on or around a structure is a sure sign of a nest close by. Letting it survive for any length of time could result in costly damage and therefore a thorough treatment of the area should be done to insure this isn't the case.

Here are direct links to the information and products listed above:

Carpenter Ant Control Article:  http://www.carpenterants.com/carpenter-ant-control

Drione Dust:  http://www.bugspray.com/catalog/products/page91.html

Termidor:  http://www.bugspray.com/item/termidor_sc.html