Anthomyia species fly on a leaf . Galicia, Spain. Photo by Raymond JC Cannon

The first time I saw a fly with a droplet of water protruding from it’s mouth (or the tip of the proboscis) I was quite surprised. Why would a fly be blowing bubbles like this?

Jean and Fred Bubble, bubble Steganopsis melanogaster (Flickr CC). https://www.flickr.com/photos/jean_hort/17624239098

It turns out that flies do this to cool down!  They move a droplet of fluid in and out and of their buccopharyngeal cavity a number of times before eventually swallowing it (Gomes et al., 2018).  This is called bubbling behaviour, which helps them lower their body temperature by evaporative cooling.

Schematic representation of-the-heat exchange dynamics-as-a-crop-fluid droplet is moved (Gomez et al., 2018)

Fully gorged flies eliminate excess water by bubbling behaviour. The evaporation of water concentrates the suspended nutrients and thereby reduces the crop volume, allowing the fly to resume fluid feeding, or minimize the water load while foraging for other resources (Hendrichs et al., 1992)..

Fly blowing bubbles by IMG_350D_16068. Flickr CC. https://www.flickr.com/photos/dincordero/543759601

As the droplet is extruded, evaporation lowers the fluid´s temperature, which, upon its re-ingestion, lowers the blowfly’s body temperature (Gomes et al., 2018).

Bubbling fly by Charles Lam. Flickr CC BY-SA 2.0. https://flickr.com/photos/49296659@N00/2635176642

Flies rarely move whilst bubbling, but if disturbed, they quickly reingest the liquid – although a few dropped their bubbles – and move off! (Stoffolano et al., 2008).

Bubble Blowing Fly Gerald Yuvallos Flickr CC. https://www.flickr.com/photos/gyuvallos/64217979/

Some Hymenoptera (bees and wasps) also reportedly engage in bubbling behaviour, and occasionally deposit the regurgitate on the substrate, followed by subsequent re‐ingestion.

Bubbling Fly. Ivicabrlic / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)+

The droplet fluid consists of a mixture of liquids from the ingested food, enzymes from the salivary glands etc., with evidence pointing to a role in liquid meal dehydration (Gomes et al., 2018).

Bubbling blow fly by Alvesgaspar (CC BY-SA 3.0) https://www.wikiwand.com/en/Regurgitation_(digestion)

 

References

Coronado-Gonzalez, P. A., Vijaysegaran, S., & Robinson, A. S. (2008). Functional morphology of the mouthparts of the adult Mediterranean fruit fly, Ceratitis capitata. Journal of Insect Science8(1).

Gomes, G., Köberle, R., Von Zuben, C. J., & Andrade, D. V. (2018). Droplet bubbling evaporatively cools a blowfly. Scientific reports8(1), 1-7.

Hendrichs, J., Cooley, S. S., & Prokopy, R. J. (1992). Post‐feeding bubbling behaviour in fluid‐feeding Diptera: concentration of crop contents by oral evaporation of excess water. Physiological entomology17(2), 153-161.

Stoffolano Jr, J. G., Acaron, A., & Conway, M. (2008). “Bubbling” or droplet regurgitation in both sexes of adult Phormia regina (Diptera: Calliphoridae) fed various concentrations of sugar and protein solutions. Annals of the Entomological Society of America101(5), 964-970.

Links and blogs on fly bubbling

https://phys.org/news/2018-04-tiny-cool.html

https://www.scimex.org/newsfeed/blow-flies-blow-spit-bubbles-and-drink-them-to-keep-cool

https://www.diptera.info/forum/viewthread.php?forum_id=16&thread_id=1016

Flies Blowing Bubbles

 

Backyard curiosities 1: Bubble-blowing flies