Question
I have an existing lilac bush that has ladybugs in the grassy area around it. Is this healthy?

Answer
Ladybugs will not harm the bush in fact they are a predator to aphids that feed on the bush. I would just leave them alone when they do not have any more insects to feed on they will go away. Some people will buy ladybugs to control aphids so you have a ready supply without paying for them.