The ants probably aren't harmful directly, but they may be farming aphids on your plants. This probably wouldn't hurt your trees, but take a close look at your strawberries to see if you notice any aphids. If you do, insecticidal soap will work.

Second, make sure they are not carpender ants. (I don't know anything about those, but I'd make sure they weren't before ignoring them). They can also be a nuisance in the kitchen where they get into food. You'll need to hire someone to make sure your house is well sealed to fix that.

However, if they are not carpender ants and you don't see them in your house or any aphids on your plants, I wouldn't worry about them. They may simply be swarming. Ants will do that sometimes, but don't seem to hurt anything except maybe a bite on your skin. :)