Journal archives for December 2021

December 04, 2021

December 24, 2021

Distinguishing Eristalis arbustorum and Eristalis abusiva

Eristalis abusiva is a rare Palearctic species of drone fly. It seems to increase in abundance towards the coast, but is found inland, and there are records from entirely landlocked countries. According to Barkalov (Checklist of the hover-flies (Diptera, Syrphidae) of Russia 2018) its range extends as far east as Japan.

As cool a species as it is, its main function in life seems to be to complicate the identification of the much more common E arbustorum, which is rather similar. Below I will give the standard means of distinguishing them and their pitfalls, but I will also try to supplement this with some thoughts of my own.

It is difficult to gauge the variability of a rare species. How many people have seen a large enough number? Here we see the value of a site like iNat, which might just have the biggest collection of abusiva specimens in the world! Male and female, and from a diversity of locations. (Still only 30 or so and counting). Some detailed pictures can also be found on Steven Falk's website

Thanks to @sbushes, @jeanpaulboerekamps, @waldgeist and @alexplayford for giving permission for me to use their pictures.

The characters covered are:
Published characters:
.1. Aristae
.2. Middle tibiae
.3. Male eyes
.4. Face stripe

Other Observations:
.5. Geography
.6. Face shape
.7. Hairiness
.8. Scutum dusting
.9. Female abdomen markings

Posted on December 24, 2021 11:17 by matthewvosper matthewvosper | 6 comments | Leave a comment

December 31, 2021

Key to the Neotropical Eristalis

Here is a key to the Eristalis of the Neotropical region.

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.

For the Nearctic Eristalis (including the northernmost states of Mexico) see the excellent key by @edanko and @zdanko.

The greatest difficulty in identifying Eristalis in this region is actually confusion with some of the many Palpada species. Bolder markings on the scutum, a bright scutellum, brighter markings generally, and thickened hind legs are all indications that you may in fact have a Palpada.

Posted on December 31, 2021 11:29 by matthewvosper matthewvosper | 9 comments | Leave a comment