Nikonian72 wrote:
These are not "bubbles" of air, rather droplets of digestive juices. Most flies do not have chewing mouth parts. Instead, their mouths are either a long, penetrating hollow proboscis, or an articulated suction tongue. Both designs ingest liquidized food of their prey, after injection or application of acidic juices.
Thanks, Douglass. Interesting subject. In an effort to properly title future posts of this behavior, I did a brief search. Seems that the term (bubbling) is used in a lot of papers describing this behavior. Remarkable that this behavior has so much documentation. Seems they do this when the liquid has a high water content. For those interested, a short quote from one source: "When the level of dilution and total volume of food ingested were great enough, engorged flies entered extended quiescent postfeeding periods during which they extrude orally droplets of liquid crop contents (“bubbling”). After this they reinitiated feeding, followed by more bubbling and feeding bouts." Read more here: