Some of these, such as A. mediata , can also be considered boreal in distribution, and good examples of species best exhibiting a Canadian or boreal faunal association are Ammophila azteca, Podalonia luctuosa , and P. robusta . Some genera that occur only in the southernmost part of the state, such as Podium and Eremnophila are predominantly tropical in origin, and appear to have reached there the limit of their northward distribution. In the case of Sphex , a widespread genus, their northward distribution appears to be determined by the presence of appropriate tettigoniid prey. Species more commonly associated with the southeastern U.S., such as Ammophila nigricans and A. pictipennis , are likewise found in the southern tiers of Michigan counties.
Faunal composition changes over time, especially as habitats are changed or destroyed.
Therefore, there are some species in threatened habitats that deserve further study. Two such species in Michigan, Ammophila cleopatra and Podalonia sericea , occur in dune habitats along Lake Michigan, and are recorded from only a few localities. Although they are widespread west of the Rockies, Michigan is their easternmost limit. Intensive searching may reveal a wider distribution, but little is really known of the habits of these wasps in Michigan. Most other species of sphecines occupy habitats that are more or less regularly disturbed.