Spanish made mosquito from mosca with a diminutive ending. Mosca goes back to Latin musca; English then borrowed mosquito.
Spanish and English use the same spelling. The puzzle ends with the Spanish formation; the borrowing into English comes next.
Sources
- Merriam-Webster: mosquito
Word History and Kids Etymology give the Latin base, Spanish formation and English borrowing.
- Cambridge Dictionary · mosquito
Meanings of the older forms on the word path.