Lady bugs eat aphids, I'm happy to see them in the garden. I guess if you had a major aphid issue you would have more lady bugs as well, but you would know if that was the case. If you have them, you'll see them on the leaves. They don't really eat the leaf like an army worm or something, they suck the juices out. I would check for beetles/worms around your plants if you have holes.
It could possibly mean that they have a food source - or it could also mean that they are congregating to mate. Although, doesn't that usually happen later in the summer? I haven't lived in a normal temperate climate zone for quite a while, so I can't really remember.