Elliott's Unofficial Revision of Rivnay's Ripiphorus Key
In progress ...
First segment of hind tarsus as long as all others, a little thicker and truncate, emarginate at apex ... aurantus
First segment of hind tarsus shorter and wider than others or longer and as slender
First segment of hind tarsus obliquely truncate and emarginate at apex, shorter than all others
First segment of hind tarsus very little thicker than others and as long or longer
Abdomen and legs straw-yellow, abdomen with varying amounts of brown/black ... rex or vierecki (syn knausi), see https://bugguide.net/node/view/643660
Abdomen orange, brown, or black
Female and male abdomen black or brown
Ripiphorus brevipes
Ripiphorus calopterus
Ripiphorus minimus
Ripiphorus nevadicus
Ripiphorus luteipennis
Ripiphorus diadasiae
Ripiphorus sexdens
Female abdomen yellow to orange, elytra hyaline to pale orange; male abdomen black or brown
Female and male abdomen orange to red, elytra similarly bright
Chihuahuan Desert and Rio Grande Valley, all but T1 entirely yellow ... neomexicanus
Colorado Plateau and Sonoran Desert, dark markings on multiple tergites ... scaber
Great Plains ... solidaginis
California and Baja Peninsula ... epinomiae
Gulf Coast (Texas to Florida) ... nomiae
Mid-Atlantic? ... semiflavus
Ripiphorus dammersi
Ripiphorus eremicola
Ripiphorus flaviventris
Ripiphorus laevicollis
Ripiphorus popenoei
Ripiphorus smithi
[Long first hind tarsal segment, female abdomen orange and brown/black]
Ripiphorus blaisdelli
Ripiphorus californicus
Ripiphorus mutchleri
Ripiphorus simplex
[Long first hind tarsal segment, female and male abdomen brown/black, wings clear]
Ripiphorus columbianus
Ripiphorus iridescens
Ripiphorus hyalinus
Ripiphorus stylopides
Ripiphorus walshi
[Long first hind tarsal segment, female and male abdomen brown/black, wings smoky]
Ripiphorus fasciatus
Ripiphorus niger
Ripiphorus schwarzi
Ripiphorus tuberculatus
Ripiphorus zeschi
Doubtful species according to Rivnay, 1929:
Ripiphorus americanus
Ripiphorus flavicornis