Dr Amnon Freidburg identified these flies as Desmometopa sp. An interesting feature of Milichiidae behavior is kleptoparasitism or commensalism. Desmometopa and several other genera suck at the prey of spiders. In almost all cases it is only the females that are kleptoparasitic. In this case, the spider had caught a bee. You can see the flies actually crawling between the legs of the spider. I took this picture near my home in Holon. Although 4 species of Desmometopa are in the collection at Bet Dagan, this genus does not yet appear in the literature of Israeliinsects.

For more information on this insect's close and distant relatives, why not visit my check-list of Israeliinsects?