I have a couple dozen large flying insects that I don't want to kill but may have to pending what you tell me. They are about 2.5 inches long w/ a head, thorax & abdomen. They are black/blue/purplish long wings attached just at the beginning of the thorax and all the way past it's tail. I believe they are a wasp of some type but are diggers. They have been there over five years but not in as great of numbers. They are along the sidewalk in the front of my house where they get a good southern exposure. I don't think they can sting but they look very intimidating. I can go stand in their midst and they a swarm in circles around me but do not bother me. I have two concerns. #1) Can they sting? #2)how much ground damage can I expect? I work very hard on my yard and where they are has only been seeded for two years. I looked through pictures to try to I.D. them myself but there are too many possibilities. They have no markings of any other colors. I found a picture that may be them. I could take pictures of the ones from my yard. They would also show the dug-up dirt. Please help I don't want to destroy them if I can help it. Thanks!

From your description this large insect is a digger wasp. Very common this time of year and in areas where they can construct burrows in the soil or under the sidewalk in your case. This wasp is closely related to the cicada killer, but usually does not make a large burrow, so the amount of soil displaced onto the surface is rather small. They can sting, but like cicada killers, one essentially has to step on one barefoot or grab one barehanded to get stung. Being a native insect, its numbers will probably plummet in the next year or two due to natural enemy attack. So you may leave them alone, there is no real need to destroy them. There are several species found in N. Illinois.