Blow flies use an unusual method to reduce their body temperature; releasing saliva droplets from their mouths and subsequently re-ingesting them, according to a study in Scientific Reports.
Guilherme Gomes and colleagues found that once a saliva droplet leaves a blow fly’s mouth, it partially evaporates and thus cools down. The re-ingestion of the droplet by the fly then reduces its body temperature. The authors found that blow flies repeated the behaviour more often as the air temperature increased, suggesting that it helps to maintain an optimum body temperature.
However, this behaviour was not observed when the blow flies were very active, which the authors suggest may be because their muscles need to be warm to be able to fly. It was also found to be ineffective in humid environments as the moisture in the air prevented the droplet from evaporating; the more humid the surroundings, the less frequently this behaviour was observed. The authors hypothesize that other insects may regulate their body temperature in similar ways, but note that this would only be effective in small animals, due to the need to produce a large enough saliva droplet relative to their body size.