Butterflies and skippers have been collected in Michigan for over 130 years and the accompanying data labels continue to provide significant information. Both collection date and site information for voucher specimens provide the data that is used to ascertain the daily maximum-minimum temperatures for the year in which the specimens were collected. This information may then be used to calculate the degree-day accumulations above a base value over those specific dates.
The Michigan Entomological Society - Michigan Lepidoptera Survey (MLS) is a team of lepidopterists who have endeavored to create a composite database of all voucher specimens in museum and private collections, published data, and submitted data, as well as from surveys conducted throughout the state. This composite data set was used to formulate a first generation of early flight periods of Michigan butterflies and skippers. Accumulated degree-days for predicting the emergence/dispersal and thus the first early flight period are presented for Michigan butterfly and skipper species and subspecies.
Perkins, Owen A.
"Using Degree-Day Methodology to Ascertain Early Flight Periods of Michigan Butterflies and Skippers,"
The Great Lakes Entomologist, vol 40
Available at: https://scholar.valpo.edu/tgle/vol40/iss2/2