Один комар сел мне на руку, когда я стоял под берёзой.

One mosquito landed on my hand when I was standing under the birch tree.

Breakdown of Один комар сел мне на руку, когда я стоял под берёзой.

• я: I
• стоять: to stand
• на: on
• когда: when

Questions & Answers about Один комар сел мне на руку, когда я стоял под берёзой.

Why does the sentence begin with Один комар? Does один just mean one here?

Yes, один literally means one, but in a sentence like this it often works like a single or one in English:

• Один комар = one mosquito / a mosquito
• It can add a slight sense of one particular mosquito or a single mosquito

Russian has no articles (a / the), so words like один can sometimes help introduce something new into the story.

Compare:

• Комар сел мне на руку = A/The mosquito landed on my hand
• Один комар сел мне на руку = One mosquito landed on my hand

So here один is not just mathematical; it also helps set the scene.

Why is комар in the form комар?

Because комар is the subject of the sentence, so it is in the nominative case.

The mosquito is the thing doing the action:

• комар = the mosquito
• сел = sat down / landed

So:

• Один комар сел... = One mosquito landed...

If the mosquito were an object instead, its form might change. But here it is the subject, so nominative is used.