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 by matthewvosper matthewvosper, 24 December, 2021 11:17

Comments

@flo-dycob @gerrit_oehm @christian_heintzen @dipterajere @erikas_diptera @ophrys I hope there's some usefulness to this if anyone needs a pointer on how to distinguish these species. Anything you think needs to change feel free to let me know.

Posted by matthewvosper 12 months ago (Flag)

Note that the '@'s on the photos function both as an attribution and as hyperlinks to the observations.

Posted by matthewvosper 12 months ago (Flag)

Nice.

At least here in the north Eristalis abusiva is not partivularly coastal ... if anything, I would say the opposite. Maybe it prefers coasts further south as they can be cooler for parts of the year, or it is just the fact that many central european countries do not (anymore) have extensive non-coastal wetlands.

Posted by dipterajere 12 months ago (Flag)

@dipterajere interesting, thanks. Some central European 'common names' (on iNat) actually translate to 'Coastal Drone Fly'. By its presence in some places though it's clear that the species does not depend on the sea being near.

Posted by matthewvosper 12 months ago (Flag)

Looking a the GBIF map (abviously not a very reliable source, but better than nothing :) ) Eristalis abusiva is all over the place in lowland North Europe: https://www.gbif.org/species/1541164.

For comparison, Eristalinus aeneus is mostly coastal in Northern Europe (but oddly not further south): https://www.gbif.org/species/1542830

Posted by dipterajere 12 months ago (Flag)

I actually think if you zoom in on the GBIF map the observations do get denser towards the coasts. E aeneus actually breeds in brackish pools I believe. I will amend the wording a bit I think, thanks!

Posted by matthewvosper 12 months ago (Flag)

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