Members of what I call the"western-montane" fauna are those species that exist in the western states and montane areas, but are found at northern latitudes east of the Rocky Mountains. Prime examples of this type of distribution are Ammophila mediata, A. cleopatra, Palmodes dimidiatus, Podalonia sericea, and non-sphecine wasps, such as Tachysphex aethiops (Cresson) (O'Brien 1987). 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. Steiner (1973) found these species as far north as the Northwest Territories and Yukon, and in Michigan they are quite widespread in the UP and northern LP, but rare in the central and southern parts of the state. 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. Some species, such as A. urnaria, may actually increase their distribution or populations when new nesting areas are created (e.g., gravel pits or dirt roads). Synanthropic species, such as Sceliphron caementarium, have probably also increased in abundance and have certainly widened their distribution as a result of human activitics.
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