They look like they鈥檙e using bubble gum. Brazilian flies blow out deep brown bubbles of spit every few seconds. Now it seems these bubbles have a serious purpose: to keep the insect cool.
of the University of S茫o Paulo in Brazil and his colleagues placed groups of 50 latrine blowflies () in transparent cylinders. Then they gradually raised the temperature inside, and took infrared images of the blowflies as they blew bubbles in and out.
As the bubbles went in and out of each fly鈥檚 proboscis, both the bubbles and the flies cooled down.
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The spit bubbles cooled because some of the liquid evaporated, which absorbed heat. On average, each bubble cooled by 8掳C in each 15-second cycle of blowing out and in.
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鈥淎fter re-ingesting a cooled droplet, the temperature of the fly鈥檚 head immediately decreases by up to 3掳C,鈥� says Gomes. Sometimes, a fly would blow a bubble out and in a dozen times. 鈥淭he more sequential cycles it performs, the more the body temperature decreases, until it reaches a balance with the surroundings.鈥�
By repeatedly blowing bubbles, flies could cool their heads, thoraxes and abdomens by as much as 3掳C, 1.6掳C and 0.8掳C respectively.
Previously, insect scientists had assumed that blowing the bubbles helped the flies digest food. Gomes says this might also be true.
The team found that flies don鈥檛 blow bubbles when they鈥檙e active, probably because their wings work best when they鈥檙e warm. Nor do they bother when the air is extremely humid, above 70 per cent relative humidity, because the clamminess prevents evaporation.
Bubble bubble
However, they do tend to blow bubbles at night. 鈥淲e speculate this behaviour saves energy by cooling the body and reducing metabolic rate,鈥� says Gomes.
Gomes says blowing cooling bubbles may be a widespread strategy used by other insects. Bumblebees, hawkmoths, mosquitoes and sawfly larvae have all been seen blowing bubbles. Other species, such as bees, spit water on each other.
Insects need tricks like these because, unlike mammals that can lose heat by evaporation 鈥� either by sweating or by licking saliva onto their limbs 鈥� they are encased in a tough exoskeleton that is impermeable to water.
Latrine blowflies are abundant worldwide and pose a threat to humans. They don鈥檛 bite, but they can spread infections to humans and animals from cadavers, faeces and rotten meat. Knowing more about how they survive could help us find ways to control them, says Gomes.
Nature Scientific Reports
