Blowflies keep their cool with drool | Science News for Students

Blowflies keep their cool with drool

Dangle, slurp, repeat may help these insects keep their brains from overheating
Feb 7, 2018 — 6:45 am EST
If this blowfly starts overheating, it has a trick for reducing its temperature. It involves drool.
Muhammad Mahdi Karim/GFDL

SAN FRANCISCO, Calif. — Blowflies don’t sweat. However, they have raised cooling by drooling to a high art.

In hot times, these sturdy, big-eyed flies repeatedly release — and then retract — a drop of cooling saliva. Denis Andrade reported the trick January 4. He was speaking at the annual meeting of the Society for Integrative and Comparative Biology. He studies ecology and evolution at the Universidade Estadual Paulista. That’s in Rio Claro, Brazil.

The fly’s technique isn’t sweating. That is what keeps people cool. Sweat evaporates taking a tiny amount of body heat with it. Blowfly droplets put the cooling power of their natural fluids to use in a different way, explains Andrade.

The saliva hangs on a fly’s mouthparts. There, the droplet starts to lose some of its heat to the air. When the droplet has cooled a bit, the fly then slurps it back in, Andrade and colleagues showed.

X-ray images showed the sucked-up droplet in the fly’s throatlike passage near the animal’s brain. The same droplet seemed to be released, cooled, drawn back in and then drooled again. The insect repeated this several times in a row.

This may prevent dangerous overheating, Andrade proposes. After several droolings, the fly’s body temp can drop up to 4 degrees Celsius (7 degrees Fahrenheit) below that of the surrounding air.

Andrade had never seen a report of this saliva droplet in-and-out technique before he and a colleague noticed it. They had been watching blowfly temperatures for other reasons. But in 2012, Chloé Lahondère and a colleague described something similar — in mosquitoes.  

These blood suckers let their body temperature rise and fall with what’s around them. But they can get a heat rush when drinking from warm-blooded mammals, like us. So while drinking, the insects release a blood-tinged drop of urine from their rear ends. That droplet sheds some of their body heat. There’s some fluid movement within the droplet, says Lahondère. (She’s now at Virginia Tech in Blacksburg.) However, she can’t say whether any of the liquid gets recaptured by the body the way fly drool is.

mosquito cooling
A mosquito has a reverse version of the blowfly trick. In a 2012 study, researchers showed how this Anopheles stephensi mosquito drinks mammal-hot blood and grows cooler (paler yellow) at the rear. That’s after the insect releases a drop of bloody urine that cools (blue) before falling and being replaced.
C. Lahondère and C.R. Lazzari/Current Biology 2012

Power Words

(more about Power Words)

biology     The study of living things. The scientists who study them are known as biologists.

colleague     Someone who works with another; a co-worker or team member.

ecology      A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).

evaporate     To turn from liquid into vapor.

insect     A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.

liquid     A material that flows freely but keeps a constant volume, like water or oil.

mammal     A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.

warm-blooded     Adjective for animals (chiefly mammals and birds) that maintain a constant body temperature, typically above that of their surroundings. Scientists generally prefer the term endothermic to describe animals that generate heat to control their body’s temperature.

X-ray     A type of radiation analogous to gamma rays, but having somewhat lower energy.


Meeting:​​ G. Gomes et al.  Stay cool with a drop of drool: evaporative cooling blowfly way. Society for Integrative and Comparative Biology 2018 annual meeting, San Francisco, January 4, 2018. 

Journal: C. Lahondère and C. Lazzari. Mosquitoes cool down during blood feeding to avoid overheating. Current Biology. Vol. 22, January 10, 2012, p. 40. doi: 10.1016/j.cub.2011.11.029.