"There is an excellent paper on 'The Eristalis Flower Flies of the Americas South of the United States' by F.C. Thompson. This covers all the species here, and includes a very useful key, as well as full descriptions of all the species. Almost all of my information comes from this paper. The Thompson key however includes some clauses not well tailored to photographic ID, and also includes a few Palpada species.

The advantages of doing another key are partly the opportunity to tailor it towards photographs, partly for accessibility, and partly as a consolidation of learning exercise for myself. The Neotropical Eristalis are mostly quite visually distinctive, and it is not necessary to resort to clauses such as 'aristae plumose or bare'.

I'm not quite covering the same area as the Thompson paper. The Mexican states bordering the USA can see species that are regarded as Nearctic: So Thompson includes E stipator, but E arbustorum is also recorded on iNat from those northern states, and there is the obvious potential for other species such as E hirta to cross the border. For that reason I'm not including the very North of Mexico: Species covered by this key are alleni, bellardii, bogotensis, circe, croceimaculata, gatesi, persa and tenax." - Matthew Vosper