The distributions of American cicada killers (Sphecius) were examined via solicited and museum specimens. S.
hogardii occurs in southern Florida and several Caribbean islands. S. speciosus occurs throughout the east coast,
southeast, and Midwestern states at high densities, and its range extends much farther west than expected, but not west of
the continental divide. S. speciosus appears to be excluded from high altitudes. S. grandis and S. convallis occur at higher
altitudes and are largely sympatric throughout the west, but are most common in lower riparian regions. Sphecius grandis
is found at significantly higher altitudes than S. convallis. Both are sympatric with S. speciosus on both sides of the Rio
Grande. The northern boundaries of Sphecius extend to 48.2°N latitude, and are associated with well known faunal zones.
The continental divide may have served as a geographic barrier, playing a role in the evolution of American Sphecius by