Until recently the species of widow spider occurring in Michigan was considered a variant of the black widow, Latrodectus mactans (Fabricius). Levi (1959) summarized and revised the worldwide genus Latrodectus, placing the southern areas of Illinois, Indiana, and Iowa as the northern limit of mactans on the North American continent. Widow spiders located north of this became part of the widespread curacaviensis group. After further information was available, McCrone and Levi (1964) revised the curacaviensis group, establishing the species that extended north of mactans as the northern widow, L. variolus, originally described by Walckenaer (183v).
L. variolus is the most northern representative of the genus in North America, but its range extends from southern Canada and the northern States south to northern Florida west through Texas to central California. It is sympatric with L. mactans in many southern states , and it is sympatric with both L. mactans and L. bishopi in Florida (McCrone and Levi, 1964).
The northern widow is known from many localities in Michigan, but in recent years it has been abundant in the northwestern part of the Lower Peninsula--particularly in Kalkaska, Grand Traverse, and Wexford counties. McCrone and Levi (1964) recorded specimens from Calhoun, Cheboygan, and Barry counties. In addition, specimens have been collected or reported from Antrim, Charlevoix, Crawford, Emmet, Livingston, Otsego, and Wayne counties. Observations were made in several localities in 1965 and 1966 in order to learn more about this spider's coloration, abundance, and habits.
Wilson, Louis F.
"The Northern Widow Spider, Latrodectus Variolus (Araneae: Theridiiae), in Michigan,"
The Great Lakes Entomologist, vol 1
Available at: https://scholar.valpo.edu/tgle/vol1/iss5/1