Blowflies （大頭蒼蠅） 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

大頭蒼蠅能夠靠自己的唾液降溫。和其他昆蟲一樣，蒼蠅是冷血?jiǎng)游?，體溫始終與周圍環(huán)境保持一致。當(dāng)天氣變得炎熱，蒼蠅的體溫會(huì)升高，但它們會(huì)利用唾液降溫。

蒼蠅會(huì)吐出一滴唾液，懸掛在口器上。當(dāng)液滴冷卻，就把它吸回來(lái)。這樣能夠防止體溫過(guò)熱。

不少動(dòng)物都會(huì)通過(guò)唾液降溫。譬如犬類會(huì)喘息吐舌或舔濕皮毛，當(dāng)唾液蒸干，便能夠幫助它們發(fā)散一些熱量。但大頭蒼蠅是唯一能夠?qū)⑼灰旱畏磸?fù)吐出、吸入，從而達(dá)到降溫效果的生物。