Millions of 17-cicadas will come out in southern Iowa in May 1963; 20,000 - 40,000 may emerge around a single tree. They won't sting or bite humans and animals or do much damage, but they will make a lot of noise.
Gunderson, Harold and Craig, W. S.
"Periodical Cicadas Are Coming in May!,"
Iowa Farm Science: Vol. 17
, Article 2.
Available at: https://lib.dr.iastate.edu/farmscience/vol17/iss10/2