Geoff can give you a more authoritative answer, but I think it's because they actually can't chew and instead use their saliva to break apart what they eat.
Nice capture.
Geoff will no doubt provide an authoritive answer but as I understand it, as Dan says,flies actually disgorge digestive juices onto their food in order to break it down into a mush which can then be sucked up.
This also explains why they can pass on pathogens to us so easily!
I still quite like photographing them regardless of their eating habits and I note that having also photographed a similar 'bubble' on occasion that it also was orange in colour!
There are a number of theories about this procedure. The most common are that it is a means of secondary digesting or a way of cooling down when their body is at risk of over heating. But there doesn't seem to be any real proof either way.
Thanks guys but it looks like the jury is still out
Indeed it is. Geoff's comment made me curious, so I looked on dipertera.info, my go-to source for all things fly-related, and found this fascinating (to me, anyway) discussion: https://diptera.info/articles.php?article_id=16. If you read it, it's worth reading to the end of the comments (there are only 7), because the last comment is very informative.
PS: You'll see a few comments by "Lord V". That's Brian Venentari (sp), in my opinion one of the foremost live-insect macro photographers working now. He sometimes posts here: https://photography-on-the.net/forum...splay.php?f=38
Last edited by DanK; 3rd March 2022 at 07:50 PM.