Journal archives for January 2024

January 06, 2024

Twelve Syrphs of Christmas! Debrief

Hello everyone,

With twelfth night come and gone, here's the wrap-up.

As you can see we've reduced the size of the 2023 pile by a little more than half (if you include the observations above genus it's just under a half, but we reduced them by a third in preparation). That's a very nice outcome. What I can't quantify is what anyone may have learned - I certainly learned plenty, and I hope some of you did too if you were involved :)

The categories that fell by more than a third were 'Xanthogramma and Doros' (-91%), Syrphus (-83%) and 'Xylotini, Myolepta' (-71%). Nice to see big proportional falls in big genera like Xylota and Syrphus, but also Eupeodes (-62%) and Eristalis (-58%).

The categories that fell by less than a third were Cheilosia (-30%), Melanostomini (-24%), Bacchini (-15%), Sphaerophoria (-13%) and 'Other Brachyopini' (-2% I guess no-one did them!). Some of these are still worth shouting about: I worked on Cheilosia and it was hard going, so a 30% fall is great, Sphaerophoria had already been reduced massively before this event (clearing up the remainder would be an easy job for someone ;) ), I think we may have been running out of steam a little/going back to work and stuff before Bacchini and Melanostomini came up, so there's a fair bit left to do on them, but still not bad at all!

My personal highlights were this Cheilosia albipila. and this Platycheirus occultus.

Hope you've had a great Christmas and New Year!

Posted on January 06, 2024 05:28 AM by matthewvosper matthewvosper | 0 comments | Leave a comment

January 20, 2024

Improving the Diversity of Hoverflies on iNatUK: Introducing "What to look out for"

One of the things that makes iNatUK's data less useful for the HRS than it might be is that there is a very strong bias towards a small number of charismatic, large and easily identified species. This is inevitable with citizen science to a degree, but doing something about it sounds like a fun challenge for us all!

To help us improve the diversity of what we observe, I have been sifting through the hoverfly records held by the NBN atlas and I plan to produce a post for each month entitled "What to Look Out For" in which I will highlight some of the seasonal species that are underrecorded in iNaturalist, but which should be identifiable from photos and are common enough to hope we could find. I intend that this will include information on how and where to find them, as well as how to identify them.

To flesh out the scale of the challenge a bit: by comparison with the more comprehensive NBN atlas database only 22 species are overrecorded on iNat! This leaves 251 species underrecorded, of which 86 have 0 observations on iNat.

One simple and general way we could improve our hoverfly diversity is by paying more attention to hoverflies in the first half of the year. Here's why I say this: The top 10 species in iNat (accounting for nearly 50% of all observations) include just one that peaks before July (and only four of the top 20) - but nearly 60% of UK species peak before July!!!

In each "What to look out for" I will list the species that are at peak abundance that month in a section called "MMM is the best month to see...", and I will also list species that are starting to increase significantly (first month at >10% of peak abundance) in a section called "MMM is the first month you might see...". I will choose a few species from each section to highlight with more information so that we can look for them intelligently - but you will also be able to look through the rest of the list for other suitable candidates. The choice of what to highlight will be based on a combination of 1) How underrecorded is the species on iNat? 2) How rare is the species? (i.e. is it realistic to think we might find some?) 3) How identifiable is it from photographs?

To each species I have attached a pair of numbers: e.g. Eristalis tenax (1,91%). The first number is the rarity expressed as a centile of abundance according to NBN: a low number suggests a common species, a number close to 100 indicates something vanishingly rare. The second number is the over/underrecordedness in iNat: A positive number indicates that the species forms a higher proportion of records in iNat than in NBN (i.e. overrecorded), and a negitive number implies that it forms a smaller proportion of iNat records than in NBN (i.e. underrecorded - a species with no iNat observations is '-100%').

To give you an idea of the rarity scale, here are a few other British species with increasing rarity values: Episyrphus balteatus (0,45%), Epistrophe eligans (10,45%), Eupeodes latifasciatus (19,-55%), Volucella inflata (31,-38%), Eriozona syrphoides (40,-64%), Pipiza luteitarsis (49,-86%), Chalcosyrphus eunotus (60,-95%), Blera fallax (77,-100%), Neocnemodon brevidens (90,-100%), Syrphus nitidifrons (100,-100%).

(Unfortunately I have not been able to find a particularly good source of information for the presence/distribution of species on the island of Ireland - so comments on distribution will only cover Great Britain. Note that fewer species are present in Ireland - obviously the commonest species in Britain are the most likely to also be present on the Emerald Isle. My apologies.)

You may want to look through the remainder of species I don't elaborate on for additional species with low rarity and significant underrecordedness, especially if you examine collected specimens - there are some extremely common species almost completely missing from iNat because they require microscopy - e.g. Neoascia podagrica (7,-98%), Syrphus vitripennis (6,-99%), Platycheirus clypeatus (8,-99%), Sphegina clunipes (20,-100%).

Hopefully this will help us improve hoverfly diversity on iNatUK, and be quite fun too!

[Boring bit: I compared iNatUK's hoverfly records for each species with the records for that species on the NBN atlas to determine whether they are under- or overreccorded on iNat. To do this I looked at the proportion of all hoverfly records that represented the species in question: if the species is a greater proportion of all hoverflies on iNat than it is on NBN I call it 'overrecorded', and 'underrecorded' if it is a smaller proportion of all hoverflies on iNat. If a species represents 1% of hoverfly records on NBN but only 0.5% on iNat it is 'underrecorded by 50%', if the same species represented 5% of hoverfly records on iNat it is 'overrecorded by 500%'. Crude, but hopefully that makes some sense.]

[Incidentally, the 22 overrecorded species are: Volucella zonaria (+1034%), Epistrophe melanostoma (+473%), Cheilosia caerulescens (+331%), Volucella inanis (+309%), Myathropa florea (174%), Merodon equestris (+169%), Eristalis similis (+155%), Eristalis tenax (+91%), Volucella pellucens (+78%), Chrysotoxum festivum (+63%), Meliscaeva auricollis (+63%), Eristalis pertinax (+57%), Dasysyrphus albostriatus (53%), Episyrphus balteatus (+45%), Epistrophe eligans (+45%), Eupeodes corollae (+39%), Epistrophella euchroma (+36%), Rhingia rostrata (+32%), Xanthogramma pedissequum (+26%), Sphaerophoria scripta (+25%), Chrysotoxum veralli (+23%) and Scaeva pyrastri (+17%). Most of these make sense as the sort of species citizen scientists like ourselves will most easily notice, others (such as Epistrophe melanostoma) seem to be there more as a quirk of small numbers. Rhingia rostrata and Cheilosia caerulescens may be there because of their recent explosion in numbers - NBN goes back to a time when they were much rarer but most of iNat's data is very recent.]

Posted on January 20, 2024 10:33 PM by matthewvosper matthewvosper | 6 comments | Leave a comment

January 23, 2024

Explorations in European Sphaerophoria

Toward the end of last year I've tried to deal with the European Sphaerophoria observations. I've added sex and life stage annotations to almost all of them except mating pairs, which I have marked with the observation field 'copulating'. Hopefully now the phenology graphs on the genus taxon page are more meaningful (especially because the 'no annotation' plot on the sex phenology graph basically corresponds to 'mating season').

I've also been rolling out the observation field 'Sphaerophoria identifiable group', which was created by @upupa-epops for North American species, but he kindly added some categories for Europe. The main aim of this really is to try and make it possible to find the things that aren't S scripta! The rules I've followed for each value are:

'cf. S scripta': for males that I suspect of being more elongate but can't properly judge the length: for females with a scripta-like marking on T5 (well separated bars terminating in distinct inward-angled longitudinal wedges).
'interrupta group': for specimens I suspect of being a spotted species, primarily interrupta, fatarum or philantha, especially if there is a strong face stripe (the spots being well formed rather than looking like darkened bands)
'Complete lateral scutum stripes': for specimens that have complete lateral stripes on the scutum but seem to not be scripta or interrupta-group
'"cleoae" pattern': for females exhibiting cleoae characteristics regardless of species (terminal tergites/sternites fused into rings, bands broken in the lateral third).

I have also added the observation field 'cf' to several observations, especially if I suspect interrupta s.s. (broad spots and strong face stripe), or taeniata (very bright; female T5 short with quite straight bars narrowly joined or nearly so by an 'isthmus' in the middle)

Highlights included iNat's first S estebani (quite probably the first live photo of that species!), and the second S loewii

"cleoae" I find quite interesting. Almost all of these I assume to be S scripta, but there is one definate S rueppellii and one probable S taeniata. I don't know how much is known about the "cleoae" phenomenon in Europe.

Posted on January 23, 2024 01:16 PM by matthewvosper matthewvosper | 1 comment | Leave a comment