What is this fly with legs like a flea?

[rjlittlefield]

This fly turned up in a number of places while my wife and I were studying a document on her computer. I first saw it visually on a book, then another book, then scurrying across a piece of paper, then another book, then... You get the idea: constantly in motion. But I'm pretty sure that before the books it was on my hand, then my neck, then my wife's arm. It was really very annoying, before it suffered a physical impact that seems to have killed it without doing much deformation.

I'm hopeful that somebody will recognize this small fly. I cannot match it to anything in my books.

In addition to the oddly thick legs, it has very long feathered arista and heavily bristled leading edge on its wings.

What is this fly, with legs like a flea?







By the way, you'll have to ignore the bright blobs on the end of the wing. When I started photographing, I noticed there was a small mite(?) running furiously back and forth on the wing. He is blurred in every image due to 1/4 second exposure time.

Edited to add: stereo of the antennae area:



--Rik

[Sym P. le]

Phorid flies, perhaps Subfamily Metopininae. I watched a related species work over some detritus once. It could practically stand on its side as it approached the detritus from every conceivable angle.

Edit: More likely Myriophora, associated with millipedes. see https://onlinelibrary.wiley.com/doi/pdf ... /cla.12189

[rjlittlefield]

Phoridae -- thank you!

In quick check at BugGuide.net, I see that Phoridae spans 43 pages of images, of which 24+ pages are identified only to family. https://en.wikipedia.org/wiki/Phoridae describes a wide range of lifestyles, from free-living in detritus to parasitoids of a wide variety of small arthropods. "The Phoridae show the greatest diversity of all the dipterous families."

None of this is encouraging about getting any more precise ID from a photo of one specimen. But sometimes I get surprised.

Sym P. le, is there something visible in this photo that suggests Myriophora vs Metopininae? Is there some particular part I might photograph, that would firm up the ID?

--Rik

[Sym P. le]

From a quick review, it seemed to me that your photos more resembled those in the posted article than any posted on bugguide. (I'm certainly not an expert)

[Sym P. le]

https://bugguide.net/node/view/40695

re: Megaselia scalaris

"... the most common species of phorid fly encountered in homes and other buildings; Phoridae specialist Brian Brown estimates that 90 percent of specimens sent to him for identification are Megaselia scalaris"

[rjlittlefield]

Adding a couple of images showing details of the thoracic bristles...

Note that this is the right side of the fly, where the wing joint is damaged so that the wing extends forward.

First, the whole frame, 1.34 mm diagonal (26.8 mm sensor diagonal at 20X optical magnification).



Then a crop, somewhat larger than actual-pixels.

[rjlittlefield]

https://bugguide.net/node/view/40695

re: Megaselia scalaris

"... the most common species of phorid fly encountered in homes and other buildings; Phoridae specialist Brian Brown estimates that 90 percent of specimens sent to him for identification are Megaselia scalaris"

Thanks for the further investigation.

I got to the same place, probably by the same route, and then I sort of jumped down the rabbit hole of species identification in Megaselia.

My impression, in brief, is that Megaselia is a mess.

Starting with this particular specimen, I notice that the bristles on the leading edge of the front wing look to be more prominent and less numerous than anything I see at BugGuide.net for Megaselia scalaris. For comparison, there's a very nice image at https://diptera.info/photogallery.php?photo_id=8786 , identified as Megaselia scalaris male. In the outer section of the margin -- the long cell that shows in my image -- the specimen at diptera.info seems to have about twice as many bristles, and proportionally smaller, compared to mine. A better match, thumbing through BugGuide, would seem to be Megaselia globipyga.

So do I have globipyga? Well, maybe. But then in looking for some better images of globipyga, I ran across a recent paper titled "A New Species of Megaselia Rondani (Diptera: Phoridae) from the Bioscan Project in Los Angeles, California, with Clarification of Confused Type Series for Two Other Species", by Emily A. Hartop, Maria A. Wong, and Charles S. Eiseman, (PROC. ENTOMOL. SOC. WASH. 118(1), 2016, pp. 93–100, currently available HERE. Its abstract begins with this:

Abstract.—The paratype series of Megaselia globipyga Borgmeier was found to contain two species, neither of which matched the holotype. The holotype of M. globipyga is here fully illustrated for clarity, and new biological and geographical data for the species are given.

OK, so not even the type series is consistent.

The article continues:

The problem of historic over-reliance on superficial characters and resulting misidentifications cannot be overstated; it is not uncommon for multiple species to have masqueraded as a single species in identified material and even type series, sometimes for decades.

It's maybe worth noting that globipyga was named in 1966, so the paratype series is about 50 years old -- neither ancient nor fresh out of a lab. We might have expected it to stand the test of time, but I guess not.

I think it's definitely worth noting that this article makes no mention of DNA. Despite the caution about "superficial characters", the methods of the paper were to photograph the specimens with modern microscopes and cameras (including a Keyence VHX-5000) and make decisions based on what anatomy was visible in the photographs.

Continuing my run down the rabbit hole, I then found an article titled "Opportunity in our Ignorance: Urban Biodiversity Study Reveals 30 New Species and One New Nearctic Record for Megaselia (Diptera: Phoridae) in Los Angeles (California, USA)" (Zootaxa 3941 (4): 451–484, http://dx.doi.org/10.11646/zootaxa.3941.4.1 , I retrieved from https://www.biotaxa.org/Zootaxa/article ... a.3941.4.1). This is a 2015 article by Emily A. Hartop, Brian V. Brown, and R. Henry L. Disney. The abstract begins:

An urban biodiversity study sampling primarily from private backyards in Los Angeles, California (USA), reveals the presence of fifty-six species of Megaselia within the first few months of sampling. Thirty of these are described as new to science: <list follows>

From the body of the article:

This project has forced us to delve into both type material and non-type historic collections of North American phorid flies. Errors and misidentifications are common, due in part to the identification of material in a dried state. Many details of Megaselia are only readily observable after specimens have been slide mounted. For example, four species were reported in the type series of a “species” mounted on pins when remounted on slides (Disney 1983). Descriptions of species from the females only, and males “identified” as that species based only on venational or superficial character sets is a problem that will likely take decades to sort out completely. Work on Megaselia must be made a priority despite these setbacks. The diversity of life histories for this largely cosmopolitan genus is tremendous and future study on the group is paramount for understanding their role in both our ecosystems and our lives.

And a final excerpt:

As work on Nearctic Region Megaselia progresses, keys to the fauna will be created. Currently, with the fauna only known from scattered sampling across the region, a key would be premature and largely incomplete.

Neither of the preceding papers mentions M. scalaris, as far as I can tell by searching the pdf's.

However, the article HERE (Arthropods, 2013, 2(1): 1-6) writes that:

The larvae of M. scalaris have been described as detritivore, parasite, facultative parasite, and parasitoid, consuming a wider spectrum of organic materials of both animal and plant origin than any other insect (Tumrasvin et al, 1997; Koller et al, 2003; Disney, 2008). As an adult, M. scalaris has been reported as a polyphagous organism, generally acting as saprophagous, sarcophagous or necrophagous (Costa et al, 2007). Therefore, it is not surprising that this species is easily maintained in laboratory conditions.

The parasitoid behaviour of the larvae of M. scalaris is most likely triggered by overcrowded conditions. Field reports have demonstrated the ability of this fly to feed on a wide range of living arthropods, including members of the following orders: Orthoptera (de Gregorio and Leonide, 1980), Diptera (Batista-Da-Silva, 2012), Lepidoptera (Ulloa and Hernandez 1981; Robinson, 1971), Coleoptera (Harrison and Gardner 1991; Arrendo-Bernal and Trujillo-Arriaga, 1994), Himenoptera (Zanon, 1991) Ixodida (Andreotti et al, 2003) and Araneae (Disney, 1994), some of which are of agronomic importance. Its extraordinary ecological plasticity has also led to the establishment of M. scalaris as a laboratory pest, having been reported to infest laboratory cultures of invertebrates such as cockroaches (Robinson, 1975; Miller, 1979), flies (Zwart et al, 2005) and triatomines (Costa et al, 2007).

This article continues,

We present here the first report of M. scalaris infesting laboratory stocks of Parastagmatoptera tessellata (Saussure and Zehntner, 1894), a common neotropical mantid from Argentina. The fly invaded meshed plastic containers where adult individuals of P. tessellata were being reared under controlled laboratory conditions. Mantids were found dead with larvae residing within their abdomen, feeding on their internal organs. Carcasses were kept, and the flies emerging from them were identified as M. scalaris according to Disney (1994).

Stepping back, it seems to me that there are at least two possibilities here. First is that M. scalaris is a devourer from Hell, capable of eating virtually anything, anywhere, any time. Another possibility -- which may in fact overlap with the first -- is that "M. scalaris" has served as a convenient handle for a rather larger collection of critters that all look enough alike to be confused, and which nobody has yet spent the resources to sort out. Given the results of the urban biodiversity study, which still was done solely on the basis of characters visible in photographs, I would be very much inclined to put my money on the second. But that's solely the idea of a reasonably informed layman; I have no special expertise in this area.

At any rate, with regard to the current specimen, I'd be comfortable saying that it's probably a Megaselia something-or-other, but certainly not beyond that.

--Rik

[Sym P. le]

The rabbit holes of ID's ... one thing I've realized from my foray into photomacrography is the amount of work that remains out standing in the field of classification. I suppose science is doing its best to prioritize based upon budgets, manpower, and methods.

One of my first macro images with my lens hack was an unidentified springtail, two steps away from my back door in suburbia. I've since tried to temper my expectations of answers to "What's this?" but usually fail.

[MarkSturtevant]

Eons ago, I was a graduate student in Entomology. The department had a "cockroach room", consisting of a room with lots of large garbage cans, each with tiers of platforms and full of cockroaches of various species. This was because one of the professors studied the neurobiology of cockroaches. Interesting place to visit. The place had some insect squatters, and by far the most dominant among these were Phorid flies, which were super abundant. They too thrived on the dog food roach chow and humid conditions. I have since thought it must have been a quirk of history that fruit flies became prominent insects used in genetics research. If T.H. Morgan (who started the business of using fruit flies) had a cockroach room nearby, he might have chosen Phorids instead.

[rjlittlefield]

A bit more explanation, before I forget...

The reason that I photographed the thoracic bristles was because of this sentence from https://en.wikipedia.org/wiki/Megaselia_scalaris :

Major bristles of body are characteristically feathered in this region; this is a characteristic unique to M. scalaris.[4]

Reference [4] goes to "Peterson. Manual of Nearctic Diptera. Vol. 2. Minister of Supply and Services, 1992. p.694".

I could not find that online, so I don't know exactly what "feathered" or "unique to M. scalaris" means. But I thought it might be helpful to have the picture, expecting that at some point either I'll get a copy of the reference or somebody else who knows this stuff will chime in.

In any case, I should point out that the images I posted of the thoracic bristles were shot using a Mitutoyo 20X NA 0.42 M Plan Apo objective, in a setup that is capable of capturing all the detail provided by the optics. This is equal or better than what you would see through a 200X compound scope. Studying the images, I do see some feathering on the major bristles. However, it's not easy to see even under these optimum conditions. I find it difficult to imagine that a manual intended for general use would describe as "characteristic" a feature that the user of the manual would struggle to see. On the other hand, the bristles are feathered.

So, feathering of the thoracic bristles is an ambiguous result.

When I set out to photograph those bristles, I thought it would be easy. After all, I had already photographed a similar view at 5X, and not much had changed.

Except it had. To avoid having the specimen dry out overnight, I had stored it in a mixture of water and isopropyl alcohol. When I went to photograph it, I could not get it to dry cleanly.

So then I switched gears and said "OK, let's shoot this immersed in fluid." But the size of the beast is awkward: too large for a well slide, too small for any of my usual chambers.

I struggled for an embarrassingly long time to figure out some simple way to make a small chamber. Finally it occurred to me that I could just Bondic a metal washer to a slide, fill the resulting chamber with fluid, and drop on a cover slip. Evaporation from the chamber is cut to zero by adding a reservoir of water around the outside, as shown here, and the narrow gap between the washer and the cover slip makes fluid movement be a non-issue. The biggest problem was that I was not using degassed fluid, so bubbles gradually formed.



By the way, I have a book on order: https://www.amazon.com/gp/product/041256520X "Scuttle Flies: The Phoridae" by H. Disney, 1994. Current list price $299 but out of stock. Amazon found me a copy in the UK for less than $30 including shipping. (No, they aren't offering any more for that price.) I'll report back after the book arrives and I've had a chance to do some reading.

--Rik

[Lou Jost]

Re degassing the water--- this used to cause me endless problems but it almost goes away completely if you use only room-temperature water or hotter water...

[rjlittlefield]

Re degassing the water--- this used to cause me endless problems but it almost goes away completely if you use only room-temperature water or hotter water...

Hot water, that sounds simple and effective.

Thanks!

--Rik

[Troels]

Interesting topic!

It shows that size matters. Anything smaller than around one 1000'th of our own size (i.e. around 2 mm) presents great difficulties in relation to our handling capabilities and also our senses. Catching, handling, preparing and examination is difficult and must involve both technologically advanced devices and specialized skills.

It is sobering to be reminded of our fragmentary taxonomic knowledge of smaller Diptera. I am told that the same could be said of the smaller parasitic Hymenoptera. Our knowledge of the biosphere and its finer connections is still fragmentary. Small organisms can be very important. The size is often compensatet for by their numbers.

That is also a reason why it so difficult to calculate a reasonable price on 'Ecosystem Services' and make serious cost benefit analyses concerning the environment. We simply can't calculate the future when nature is involved. We have to be cautious.

[Lou Jost]

And sadly, real taxonomists are almost extinct, except for DNA analyzers.

Sadly, DNA analysis itself is far from foolproof. Even when the sample size is large enough to give us the right topology of the phylogenetic tree for a given gene (the trees may vary from gene to gene). we still need to decide where to "cut" the branches of the tree to define the species. For poorly known organisms, where we have small samples, no ecological information, no breeding information, and incomplete geographical knowledge, it is very hard to distinguish individual variation within species from variation between species. Often (as in fungi) an arbitrary percentage of sequence differentiation is used as a theshhold to define different species. But this is somewhat unsatisfying and can be wrong.

What we would really like to know, at least for sexual organisms like flies, is whether two forms (candidate species) are freely exchanging genes when they overlap spatially. If so, they are not good species under most biolgical species concepts. But how can we apply this to populations that don't overlap? If we have big samples of each form, we can use population genetics to check for gene exchange, but it is rare to have such large samples. And what if we can show that they are not currently exchanging genes? That criterion would make every temporarily isolated population a new "species".

My solution to this problem is to take timescale into account in gene flow. The Andean environment where I work is very dynamic. Ice ages and hot periods are common, so populations have to move up and down mountains to stay at their optimal temperature. As different populations go down to lower elevations, they come into contact with other populations were formerly isolated from them. If those populations interbreed during these warm periods (and this can be checked by population genetics analyses; I've derived a differentiation measure that is linear in the divergence time between populations), then their present reproductive isolation is only temporary, and they should not be considered "good" species.

Short version-- good taxonomy is hard, and morphological traits without ecological or population-level analyses are not necessarily definitive. A partial exception is the genitalia of insects; if these differ enough between populations, then we know that it would be physically impossible for them to interbreed, and so these would be good species, with no need for further analyses. Hence entomologists' fixation on genitalia.

[rjlittlefield]

All good points! Thanks to everyone for the further thoughts.

--Rik