Last "swarm" here they killed off many branches on our blue berry bushes. I saw a few emerging last May or June. I suppose they will be bad again soon 2021 here.. I remember about 1987 they were so bad in Arlington VA and around DC, that the road in Rock Creek park was closed due to folks sliding off the road on slick "cicada slurry" because of all the bugs that were run over on the road under the trees. The May flies on the Rt 462 (Wrightsville to Columbia) bridge are not near as bad.