Drool Is Cool For Flies

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，蒼蠅是冷血動物，體溫始終與周圍環境保持一致。當天氣變得炎熱，蒼蠅的體溫會升高，但它們會利用唾液降溫。

蒼蠅會吐出一滴唾液，懸掛在口器上。當液滴冷卻，就把它吸回來。這樣能夠防止體溫過熱。

不少動物都會通過唾液降溫。譬如犬類會喘息吐舌或舔濕皮毛，當唾液蒸干，便能夠幫助它們發散一些熱量。但大頭蒼蠅是唯一能夠將同一液滴反復吐出、吸入，從而達到降溫效果的生物。