The Spanish word 'mosca' meaning 'fly' (the insect) comes directly from the Latin word 'musca', which had the same meaning. The Latin 'musca' existed alongside the Ancient Greek word 'muia' (μυῖα), also meaning 'fly'. The word underwent a minor vowel change from Latin 'u' to Spanish 'o', which was a common sound change in the development of Spanish from Latin.

The word 'mosca' is fairly basic in Spanish and is commonly used. It has given rise to related words like 'mosquito' (literally meaning 'little fly'), which has been borrowed into English with the same meaning. Another related Spanish word is 'moscatel', referring to a type of sweet wine or grape, named because flies are particularly attracted to its sweetness.

While English 'fly' comes from a different root, English has borrowed several words related to the Latin 'musca'. The most obvious is 'mosquito', which came into English through Spanish. We also see this root in scientific terms like 'muscoid' (fly-like) and in 'muscarine', a toxic compound first isolated from a fly agaric mushroom.