Two Arizona Argia species that look alike and are often found together are the Aztec Dancer, A. nahuana and California Dancer, A. agrioides.
In the hand, males of the two species can be easily separated by examination of their appendages. In the field, the most reliable character is thought to be the black mark on the second abdominal segment (S2): round spot in Aztec Dancer vs. elongated stripe in California Dancer (Paulson 2009).
On 14 October 2012 a male was found in Hot Springs Canyon, Cochise Co., AZ, that presented the "typical" S2 black mark of California Dancer, but was determined to be an Aztec Dancer based on appendage structure (pictures below). A similarly marked Aztec Dancer was recently discovered at another AZ location by Doug Danforth and Richard Bailowitz (personal communication). We may need to revisit the generality of the conclusion that the two species can be identified visually based solely on examination of the S2 black mark.
Other News About This Species
October 24, 2014
March 16, 2013
March 24, 2012
December 21, 2008