Drool Is Cool For Flies

Blowflies （大头苍蝇） use their own drool1 to stay cool. Like all insects， flies are cold-blooded （冷血的）， so their body temperature matches2 the outside temperature. When it is very warm， the flies overheat， but they can cool off using their saliva （唾液）.

A fly spits3 out a drop of saliva， holds the drop outside its mouth and the drop cools down. Then the fly slurps4 it back up. The saliva cools the flys body.

Other animals also use saliva to keep cool. Dogs pant5 or lick their fur when they got hot. They cool down as the saliva dries up. But blowflies are the only living things known to move saliva in and out of their mouth to stay cool.

口水降溫

大头苍蝇能够靠自己的唾液降温。和其他昆虫一样，苍蝇是冷血动物，体温始终与周围环境保持一致。当天气变得炎热，苍蝇的体温会升高，但它们会利用唾液降温。

苍蝇会吐出一滴唾液，悬挂在口器上。当液滴冷却，就把它吸回来。这样能够防止体温过热。

不少动物都会通过唾液降温。譬如犬类会喘息吐舌或舔湿皮毛，当唾液蒸干，便能够帮助它们发散一些热量。但大头苍蝇是唯一能够将同一液滴反复吐出、吸入，从而达到降温效果的生物。