Bubbling or Droplet Regurgitation

I observed this behavior while walking on the boardwalk at Loxahatchee. The sun light was concentrated on a particular bush and I noticed an unusual amount of fly activity (house flies, green flies, etc.).

These flies were landing in direct sunlight. I was able to first notice this "bubbling" behavior by using my 90mm macro lens with full extension tube set.

The liquid was not actually being deposited on the plant. Instead after various durations I would see these flies re-ingest the liquid and repeat the process.

One explanation for this behavior is that it concentrates the fly’s meal by evaporation.

The fly regurgitates the liquid portion of the food, holds it whilst evaporation reduces the water content and the fly then swallows a much more concentrated food meal without the water content. This continues until sufficient amount of liquid is left for the fly.

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