It is not clear which species of Ceuthophilus is most common in Iowa. At one point, iNaturalist was suggesting C. maculatus for most Ceuthophilus observations, which made it seem like C. maculatus was the most common species. As a consequence, this species is listed first in this Guide and serves as an introduction to Ceuthophilus in Iowa.
C. maculatus has a wide distribution and is common in some places, but has been misidentified for other species in the past. However, Hubbell (1936) says this species is "easily distinguished" and lists several characters. Line drawings from Hubbell (1936) for the caudal tibia, last abdominal tergite, and subgenital plate have been reproduced in the photo section (It is my understanding that copyright has expired). These images can also be seen at Orthoptera Species File. An diagram from Hubbell (1936) showing terminalia nomenclature is also included.
Hubbell's characters (these are only for males):
Abbreviations in the terminalia diagram: SG = subgenital plate, 9th = 9th abdominal tergite, ce = cercus, pa = paraproct, pst = pseudosternite, ep = epiproct. The terminalia pictured are from C. pallidipes.
As far as I can tell, each of these characters is unique to C. maculatus and one or two are probably sufficient for identification.
Coloration is variable. In general, coloration is yellowish to blackish brown above with lighter colored spots. Often there is a paler mid-dorsal stripe.
Some good example observations (note especially the curved tibia near the "knee"):
https://www.inaturalist.org/observations/81507145
https://www.inaturalist.org/observations/85855398
Bland, R.G. 2003. The Orthoptera of Michigan – Biology, Keys, and Descriptions of Grasshoppers, Katydids, and Crickets. Michigan State University Extension, Extension Bulletin E-2815. https://archive.lib.msu.edu/DMC/Ag.%20Ext.%202007-Chelsie/PDF/e2815.pdf
Vickery, V.R. and Kevan, D.K., 1985. The grasshoppers, crickets, and related insects of Canada and adjacent regions. Ulonata: Dermaptera, Cheleutoptera, Notoptera, Dictuoptera, Grylloptera, and Orthoptera. Insects and Arachnids of Canada, Part 14. Agriculture Canada. https://publications.gc.ca/collections/collection_2016/aac-aafc/agrhist/A42-42-1985-14-eng.pdf
Orthoptera Species File: http://orthoptera.speciesfile.org/Common/basic/Taxa.aspx?TaxonNameID=1130175
Hubbell, T.H., 1936. A monographic revision of the genus Ceuthophilus (Orthoptera, Gryllacrididae, Rhaphidophorinae) (Vol. 2, No. 1). University of Florida.
This species ranges across the northern U.S. from Maine to Minnesota and adjacent states in southern Canada. It occurs south to Virginia and southern Illinois. In Iowa, it occurs statewide, except for perhaps the southwest corner.
Found under stones, logs, etc., usually in forested areas. Hubbell (1936) was a little puzzled by it's habitat preferences and believed it to most common in northern prairie region in drier woodlands and less common elsewhere in its range.