We have them here in upstate New York (not so many as your picture above though). They do get
in the house, but it's not like they bite or anything. To keep pollution down and care for the Earth and all its creatures (which are not always so pretty but most serve some function) it's best not to use harsh chemical sprays. They can and do fly but if they're causing a real problem and they're all clustered as shown above, it seems like it would be a pretty easy matter to catch a large amount of them in an insect net and then drown them. I would consult with your local cooperative extension.