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All Rhizophagus spp. have antennal grooves on either side and slightly under the head (Bousquet, 2004). Body is fairly flattened, elongate and small, under 4.5 mm in total length (Bousquet, 2004). The final abdominal tergite (the last segment visible dorsally) is not covered by elytra (Sengupta, 1988). Larvae may be 2-6 mm in length and flat or cylindrical or tapered at both ends (Lawrence, 1991). There is an inward projection of the exoskeleton on the anterior segment of the underside of the thorax. The pronotum (section of exoskeleton directly behind the head) is covered in divets, and these divets are smaller than in comparable species (Bousquet, 1990). The elytra, or exoskeleton covering the hindwings, tend to be reddish at their base and get progressively darker brown moving back (Bousquet, 1990). Differences in the aedeagus (male copulatory organ) are also of use if identification is questioned (Bousquet, 1990).

This taxon is very widespread with variable traits across North America. Eastern specimens are more often found on deciduous trees (eg. maple), than in the west where the dominant host is lodgepole pine (Pinus contorta Dougl.) (Bousquet, 1990). Rhizophagus dimidiatus have been found in ex-galleries of two bark beetle species Dendroctonus rufipennis and Dendroctonus ponderosae (mountain pine beetle). Catch in window traps in forested northern Alberta is the most abundant from mid to late July (J. Jacobs, pers. comm.).

Rhizophagus dimidiatus most likely feeds on fungus present on decaying coniferous trees and may is predatory toward bark beetles or their larvae, specifically D. rufipennis and D. ponderosae (characters of Rhizophagus, Peacock, 1977; Bousquet, 1990). Considering that this same species is found under the bark of deciduous trees as well in eastern Canada, it is likely that their feeding preferences are more general than specific.

This species is found coastally and slightly inland across North America, in the east from Newfoundland and Nova Scotia south to Vermont and Tennessee, and in the west from Alaska south along the coast to California, and slightly inland from the Rocky Mountains south to Arizona and Texas (Bousquet, 1990).