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Female swarms of Phalacrotophora (Phoridae)
In June and July, I spotted a swarm of Phalacrotophora (Phoridae) flying about the bases of Acer pseudoplatanus and Fraxinus excelsior trees in mixed woodland near Norwich, England. Phalacrotophora swarms have been recorded before, but their function has always been a bit of a mystery. I identified the flies as Phalacrotophora delageae Disney, a species that has not been found in Britain before.
I will be writing a short paper adding this species to the British fauna, and describing my observations, but seems to be the perfect place to post a series of photographs which will be too costly to publish in a journal!

The swarms consisted of twenty to thirty females flying between 0.2 and 1 metres above the ground, and within 0.2 metres of the trunk. When undisturbed, up to ten females would settle on the tree trunk, in a ?head-down? posture, eaching one staying like this for up to a minute before settling elsewhere or joining the swarm again. In the ?head-down? posture, the flies extend the abdomen and point it torwards the tree, exposing the membranous patch at the base of the fifth tergite

This photo shows the 'display posture' of a Phalacrotophora delageae female.

The unchitinised part of the tergite appears to glow brightly. It contrasts with the black tergites 2 to 4 in front and the orange of the remainder of the fifth segment.

If the overall brightness is digitally reduced, you can see how much this little fly appears to glow in the dark! I did examine some live specimens in the dark, and under an ultra-violet lamp, but there was no evidence of luminescence or enhanced reflection with UV.

While sitting in this pose, the females vibrate their wings, presumably creating a distinctive sound. Visually this appears to be exactly the same as the wing-waving of Drosophila when it is 'singing'. This sequence shows the position of the wings at different points in the 'song'.

After a while, the females stop their display and sit on projections on the tree trunk (in this case a snail shell) where they interact in a casual way. Then they join the swarm again before landing in the display posture for another session.

I did not see any males at the swarming sites, and could not find any concentrations of coccinellid larvae or pupae close by. So the purpose of these female Phalacrotophora swarms is still a bit of a mystery, but I think that the visually striking display posture, combined with the 'song' and possibly pheromones must be to attract a mate.

After all, to a male Phalacrotophora this female can only be saying 'Come and get me!'

#1 | Robert Nash on 14 July 2006 15:37:30
Wonderfully observed and photographedPfftPfftPfft. I wonder if the glow protects them from predators and "parasitic" Hymenoptera, prior to dispersal and egg laying? explaining the absence of males.
Also have you seen Scrambled paper entitled Phototropism, Bioluminescence, and the Diptera? Robert
#2 | Nikita Vikhrev on 07 August 2006 13:23:12
I think that the age of scientific information on paper is over. Internet permits to get information much faster, it also permits properly illustrate it (as in this case) and immediately get comments. I think that shows all nesessary characteristics to turn into virtual dipterology jornal.
#3 | Paul Beuk on 07 August 2006 19:10:59
Still, the internet may go down, websites may go offline (God forbid that this one will) but paper publications will be available for centuries to come. I am in favour that information never will be trusted to the internet only.
#4 | conopid on 07 August 2006 20:37:25
Unless people print it off and keep it in a library maybe?!
#5 | Nikita Vikhrev on 07 August 2006 21:06:19
Anyway, it isn't we who decide the future of paper-jornals. But we can make internet jornal never mind "instead of" or "in addition to".
#6 | Robert Nash on 09 September 2006 14:36:42
REFERENCE Bioluminescence in Mycetophilidae
A pdf Pfft Suggests the light is a prey lure (interesting in view of the fact that many Phoridae are sarcosaprophagous (see Glossary) also states that the light may attract parasites (quite contrary to my suggestion). Are we getting close Tony ? Is this a death trap?
#7 | yaguza on 20 October 2006 13:06:06
Very interestingPfft
To find out how swarm works, Why don't release some male Phoridae nearby, to see if they are lured
#8 | flycatcher on 22 October 2006 23:45:15
Hello Tony,

Very interesting notes and photos. Can you tell me what camera, lens etc. you used.


John Flynn
#9 | Bastiaan Wakkie on 27 February 2007 00:39:23
To comment on the digital scientific information. How about video material? You cant really print this. Like flight or mating behavior.
You just need to backup your digital information properly. And if you allow people to download your digital info the data is spread over the world anyway. I rather have all printed material digital than the opposite I must say. So I can find information much quicker.

But then again trusting on internet solely will not be a good idea for now if your system cant handle 100% availability. (printed papers aren't always available either btw)

Some of my thoughts Wink

#10 | Toby on 31 March 2007 22:41:22
flycatcher - if you right click on top images and then click on EXIF you will see a Canon 350D digital dslr was used with a 60mm lens - probably a CAnon 60mm macro.
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17.08.23 15:23

17.08.23 13:54
Tony, I HAD a blank in the file name. Sorry!

17.08.23 13:44
Tony, thanks! I tried it (see "Cylindromyia" Wink but don't see the image in the post.

17.08.23 11:37
pjt - just send the post and attached image. Do not preview thread, as this will lose the link to the image,

16.08.23 08:37
Tried to attach an image to a forum post. jpg, 32kB, 72dpi, no blanks, ... File name is correctly displayed, but when I click "Preview Thread" it just vanishes. Help!

23.02.23 21:29
Has anyone used the Leica DM500, any comments.

27.12.22 21:10
Thanks, Jan Willem! Much appreciated. Grin

19.12.22 11:33
Thanks Paul for your work on keeping this forum available! Just made a donation via PayPal.

09.10.22 17:07
Yes, dipterologists from far abroad, please buy your copy at veldshop. Stamps will be expensive, but he, the book is unreasonably cheap Smile

07.10.22 11:55
Can any1 help out with a pdf copy of 1941 Hammer. Vidensk. Meddel. Dansk Naturhist. Foren. 105; thank you

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