Excerpt: I have recently plotted the known Michigan distribution of the various species of Orthoptera which occur in the state (Cantrall, 1968). When this distribution of any single form is compared with its range, it is usually quite clear by what path the insect reached Michigan.
Cantrall, Irving J.
"Appalachian Orthopteron Relicts in Michigan,"
The Great Lakes Entomologist: Vol. 3
, Article 2.
Available at: http://scholar.valpo.edu/tgle/vol3/iss3/2