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Hi,
I am very curious what these tiny flies with the size of fruitflies could be so interested in the unfortunate prey of the zebraspider, not fearing the spider, I have seen these flies also on other occasions like on the prey of a huge robberfly.

Very strange..any chance for a family or genus name?
Thank you!
Myriam:)

Botanical garden Rio de Janeiro, January 2010

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Looks like to Chloropidae...

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Thanks Sara!
Any idea why they are interested in the spider's prey?

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I don't have species idea, but if it be Chloropidae, I just know that [some] species of Chloropidae interested to the secretion fluid that exit from body, maybe that such things...I await for suitable answer...

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Milichiidae are know for this behaviour, but I can't tell them apart from Chloropidae :D

Edit: http://milichiidae.info/

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Thank you very much for your inform;B)
But this behavior in Chloropidae is, too;
For example: Siphunculina or Hippelates…and a few species that now I don’t remember (if remember it, I’ll tell you), have such behavior, which in some that species, even maybe cause disease in human… ;)

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Gaurax and Trachysiphonella are two genera of chloropids that have been observed feeding on crab spider prey.

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Thank you Tony! :)

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Thank you all for the info!:)
It is still mysterious though why they only feed on the prey when caught by a predator. It is creepy and they look so innocent!:S

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If the prey are Heteroptera, the flies are attracted by the chemicals in the defensive spray of the bugs.

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Hi Myriam

I don't know you still are curious about this subject or you found any answer about, (of course I'll be glad if you advise me about result that you found) :) , anyway I thought maybe interesting for you if you look at this http://www.fcla.e...82p179.pdf! :)

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Chloropidae, Oscinellinae, Tricimba sp. Tricimba Lioy, 1864 is one of the most species rich genus in Chloropidae, 197 valid species are known. Three impressed longitudinal lines on the scutum are peculiar along which the acrostichal setulae are criss-cross orientated. Many Tricimba species visit predatory arthropods to suck the liquidated prey. An article on kleptoparasitism of Chloropidae: Tschirnhaus, M. von, Borkenstein, A. & Jödicke, R. 2015. Lestes dryas (Odonata: Lestidae) und kommensalische Fliegen (Diptera: Chloropidae), mit einer Übersicht über Kleptoparasitismus bei Halmfliegen. [Lestes dryas (Odonata: Lestidae) and commensalic flies (Diptera: Chloropidae), with an overview on kleptoparasitism of frit flies]. Mercuriale 12 (2014): 1-12; Karlsruhe.