Photographed this little Tephritidae Dioxyna bidentis cleaning its wings and blowing a bubble. Seems to be stretching the mouthparts a fair bit to get the bubble out, but it is quite large in comparison with the head
As a new member I have read this thread with great interest. At the present stage of the discussion, the 'aid to digestion' theory seems the most plausible. Is anything known about the chemistry of external digestion? Is it possible that an enzyme in the digestive juices is synthesised or activated more efficiently under UV or other radiation? (LordV hinted at something similar in post #20.) If so, flies may have evolved to bubble when fresh supplies are required and they feel safe enough (and they may occasionally do it when there isn't much radiation about, on the grounds that a little is better than nothing). Is the saliva for external digestion distinct from the stomach juices, and if so is there a reservoir for it big enough to contain a bubble?
) I named this one "the entertainer" for obvious reasons.
