@NicholasP:
Lasius spp. generally fly late August - early September, with some as late as early October.
However, L. interjectus seems to overwinter in the nest and flies in mid-late spring, alates sometimes appearing in basements in winter!
L. americanus (formerly known as L. alienus) flies in August and typically is done flying by the time the late August fliers emerge.
When in Michigan, track down the publications of Dr. Mary Talbot, which contain abundant natural history information on most ants from there.
In particular, look for her final publication, a grand summary of her 26 year study, published as "Miscellaneous Publications, Museum of Zoology, University of Michigan, No. 202".