Learn Spanish (Latin America): La mosca empieza a comer cuando encuentra comida. - The fly starts to eat when it finds food.

We use the indicative mood after cuando (when) because this sentence describes a habitual action or a general fact. The fly always starts to eat when it finds food. If this were a future, uncompleted action (like "The fly will eat when it finds food"), you would need the subjunctive encuentre.

Why is there an a between empieza and comer?

The verb empezar (to begin/start) requires the preposition a when it is followed by an infinitive verb. You will always use the formula empezar a + infinitive to say that someone starts doing something.

Why isn't there a word for "it" before encuentra?

In Spanish, subject pronouns are usually dropped when the context makes it clear who is performing the action. Since la mosca is already established as the subject in the first half of the sentence, adding a pronoun like ella before encuentra is unnecessary and would sound unnatural.

Could I use comienza instead of empieza here?