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A housefly is the ordinary small fly that comes into people’s houses — grey, busy, landing on food. The everyday word is just fly; housefly is the more exact name for that common indoor kind (the one scientists call Musca domestica), not a butterfly, not a big biting . It lays eggs in rubbish and animal waste, and that is why people chase it off the table. The word is plain and a little textbook-like: at home you say “there’s a fly in the kitchen,” not usually “a housefly,” unless you are naming the type. Dutch, Danish, Swedish and Faroese have matching compounds built the same way, which is a hint that the idea “the fly of the house” is an old, shared one in those languages.
家蠅（口語多半就叫蒼蠅）
組成house + fly. Fly here is the insect, not the verb “to fly.” Dutch huisvlieg, Danish husflue, Swedish husfluga and Faroese húsfluga are built the same way.
原始詞典資料2 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
houseflynoun
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Any fly regularly found in human dwellings.
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Any fly regularly found in human dwellings.
- Of the three potential means (carriage on the body and legs, regurgitation and defecation) by which houseflies can transmit pathogens, one involves passage through the gut. During passage through the housefly, pathogens may replicate within the gut.
- In the housefly, M. domestica, sex pheromone production is correlated with egg development.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。