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As I work in the department of invertebrate zoology in the research centre of the National Museum of Natural History, it occurs oftentimes that people contact us when they observe insects or other invertebrates in their homes.

Yesterday a man from Echternach (east Luxembourg, in the valley of the river Sauer) asked about help because he had observed a great mass of small flies in his garret.
I betook myself to the place to get an idea of the case.
An really, I have never seen such extreme gatherings of flies before. They really blackened great parts of the Windows. Despite their small size of about 2-3mm, they even produced remarquable noise as millards of them whirred all around us. I was so angry that I unfortunately did not have my camera with me....

After some researches (i did not know this phenomenom before), i found out that it must be the question of the familiy Chloropidae, most likely the genus Thaumatomyia.
I wanted to know whether T. notata is the only species to come into consideration for such mass occurences in central Europe?
If not, how could I identify the exact species? I have collected some millions of individuals, so if necessary I can take photographs of them. May be even taken under magnifying glass (but there I would have to ask a colleague from another department).

I would be very thankful for further information.
In any case, I am glad to have again something more about flies.

Thank you very much in advance for every supplemetary information.

best greetings,

Svenja Christian