Mating pairs of Xylomya tenthredinoides versus simillima

I previously separated these two species by the amount of red on the hind femur, but photos of mating pairs suggest this isn't a reliable distinction. The following linked mating pairs appear to represent the below species:

X. tenthredinoides
https://www.inaturalist.org/observations/85560188
https://bugguide.net/node/view/1617071/bgimage

X. simillima
https://www.inaturalist.org/observations/48384345
https://www.inaturalist.org/observations/80618876
https://www.inaturalist.org/observations/81167694
https://bugguide.net/node/view/57358/bgimage
https://bugguide.net/node/view/404652/bgimage
https://bugguide.net/node/view/875104/bgimage
https://bugguide.net/node/view/57359/bgimage
https://bugguide.net/node/view/406169/bgimage

Based on these observations and consulting Webb 1984, I propose the following differential diagnosis for the two species:

Posted on Αύγουστος 03, 2021 0112 ΠΜ by edanko