LordV wrote:
New theory on this behaviour. ...Wonder if it's a way of warming up faster by letting the drop warm up in the sun and then sucking it back in again. Another reason for wondering this is normally flies seem to to sunbathe with their back to the sun (ie head away from the sun), whilst when they are bubble blowing they always seem to be facing the sun or at least at right angles to it, so the bubble is getting full sun.
Brian V.

LordV wrote:
Tyhanks Dima.
Having seen some more flies doing this especially one where the bubble got very viscous and almost looked semi solid, I've reached the conclusion that the thermoregulation hypothesis is wrong. It is much more likely that they are doing the same as bees do and actually concentrating the contents by evaporation.
Brian V.

Kahis wrote:
It's time for yet another hypothesis The food is exposed to air leading to modifications in it's chemical composition by oxygenation. This would also radically change the microbial fauna of the liquid as most bacteria of the alimentary canal are anaerobic and will quickly perish when exposed to the terrible poison gas called oxygen

LordV wrote:
Ok just to shoot myself in the foot, spotted a Scatophaga stercoria bubble blowing this AM at an angle of about 120' from where the sun would have been if it was shining.
Maybe it's the IR radiation that's important .

Dima DD wrote:
I can not say which hypothesis is correct. However, I would like to put some words about this branch. In fact, body of the fly is darker and absorbs much more radiation than shining droplet. Moreover, evaporation of water from the surface must decrease droplet temperature, not warm it. More intensive evaporation - less the droplet temperature. Therefore, according to this branch of hypotheses ("thermoregulative"...), fly can use bubbling for cooling of its overheated body (i.e. it is some kind of "perspiration" ).

Susan R Walter wrote:
I watched a female Muscina sp blowing bubbles this morning. This is the first time I have witnessed this behaviour, but thanks to this forum, I immediately recognised what she was doing and stayed to watch. The droplets she produced were translucent blue grey (maybe only a reflection off her body). The droplet slowly grew to a couple of millimetres across then she slowly withdrew it, then the process was repeated. She was sitting in the sun, head to the east, on a bramble leaf. The droplet itself, because of the angle of the leaf, was not in the sun, but shaded by her body. I didn't have a camera with me, so no photo (and anyway, my photographic skills aren't good enough to add anything to these terrific images).

I am also struck by something Totipotent touched on earlier - in this case, and in each of the pictures in this thread the bubbler is female.